Definition

Bullying is defined as “a negative behaviour that (a) is intentional (perpetrators know/understand that their behaviour is unpleasant or hurtful to the target); b) is usually repetitive; and c) involves some degree of power imbalance between the targeted individual and the perpetrator(s) in favour of the latter” (Olweus & Limber, 2019).  Olweus & Limber further clarify that “the repetitive nature of the phenomenon also connotes the existence of a kind of a relationship, implying that the target individuals typically have at least some superficial knowledge of their perpetrator(s)”. Bullying can take different forms, such as physical (e.g., hitting, kicking, pushing), verbal (e.g., name-calling), relational (e.g., social exclusion, spreading false rumours or lies, friendship withdrawal threat) and/or property attacks (e.g., taking something without permission, trying to break/damage something).

Participants can be involved as bullying perpetrators (i.e., those who initiate the bullying act), victims of bullying (i.e., those who are the targets of bullying), bystanders – including assistants (e.g., those who follow the bullying perpetrator), reinforcers (e.g., those who laugh at what is happening), defenders (e.g., those who are supportive of the victim) or outsiders (e.g., those who stay away from the bullying situation) (Salmivalli et al., 1996). Generally, youth exposed to bullying have difficulty in defending themselves (Olweus, 1983). Youth who bully are considered to use aggression in a proactive and strategic manner. Some youth involved in bullying are both perpetrators and targets of bullying (often referred to as “bully-victims”). Bully-victims tend to use aggression for retaliation, but do not succeed in stopping bullying (Arseneault, 2018). Perpetrators and victims of bullying usually either keep their role over time or become uninvolved, while bully-victims tend to transition frequently between perpetrator and victim roles (Zych et al., 2020).

Prevalence

Across cultures and countries, about 30%-36% of youth aged 12-18 years old report being bullied and about 35% report having bullied others at some point during their schooling (Biswas et al., 2020; Modecki et al., 2014; UNESCO, 2019). When the frequency of being bullied is considered, 19% of youth report being bullied on one or two days and 7% on six or more days in the previous month (UNESCO, 2019). In England, according to the Department of Education, in 2017-2018, around 17% of young people had been bullied in a way that made them frightened or upset during the past 12 months. The proportion of young people reporting being bullied was higher in the younger age groups: 22% of 10-year-olds surveyed reported being bullied, whilst only 8% of 15-year-olds reported being bullied (Department of Education, 2019). While for most children bullying victimization is a transitory experience, some children are exposed to bullying over long periods of time (Oncioiu et al., 2020) or to poly-victimization (i.e., bullying alongside other forms of victimization, such as parental maltreatment or dating violence) (Finkelhor et al., 2007). Globally, prevalence rates of bullying victimization are similar among boys and girls, but variations by country and region exist (UNESCO, 2019). Boys report slightly higher rates of bullying victimization than girls in all regions except North America and sub-Saharan Africa. Boys are more likely to experience physical bullying, while girls are more likely to experience psychological bullying (e.g., subject to name-calling, rumours/lies, being left out). The prevalence of bullying perpetration is typically higher among boys (UNESCO, 2019). Moreover, certain youth are more likely to be targeted by bullying, such as those with disabilities (visible and non-visible), special educational needs, chronic conditions (e.g., psychiatric diagnoses, chronic illnesses) or LGBTQ+ youth, so the prevalence of bullying victimization can be higher in these groups than in the general population (Sentenac et al., 2012; Department of Education, 2019; Kann, 2016; UNESCO, 2016, 2021).

Assessment

In population-based studies, school surveys and prevalence studies, bullying involvement is usually measured through self-reports (Vivolo-Kantor et al., 2014). Typically, in studies where reports from several informants are available (e.g., children’s, parents’, and teachers’ reports, and peer nominations), the cross-informant agreement is low (Rønning et al., 2009; Wienke Totura et al., 2009, Shakoor et al., 2011). The low agreement between the informants is likely to reflect different sources of information that the respondents have access to. For instance, self-reports assess bullying involvement across multiple contexts (e.g., classroom, school playground, bus) and may capture experiences that are harder to observe by teachers/parents (e.g., relational bullying). Teachers and peers witness bullying involvement at school, while parents may witness it at home or hear about it from their children. However, despite low correlation, the different informants’ reports on bullying victimization show generally the same direction of association with youth’s behavioural and emotional problems or educational attainment, even if the strength of the associations may vary (Rønning et al., 2009; Wienke Totura et al., 2009; Armitage et al., 2022). This suggests that each informant contributes a unique and valid perspective on children’s bullying involvement.

The bullying questionnaires usually assess the frequency of bullying involvement by providing a definition of what bullying is and/or using items that describe bullying behaviour (e.g., pushed, hit, called names, excluded from the group). According to Olweus’ definition, the central feature that distinguishes bullying victimization from other types of peer victimization is the existence of a real or perceived power imbalance between the perpetrator and the target (Olweus, 2013). However, studies rarely directly assess power imbalance and youth’s own definitions of bullying tend to focus on the repetition of negative/harmful acts by peers, rather than the power imbalance (Green et al., 2013; Vaillancourt, McDougall, et al., 2008). In the current guide we include studies which measured both bullying involvement and peer victimization and peer aggression, but for simplicity we use only the term “bullying”.

Cyberbullying

The guide covers only traditional bullying (i.e., face-to-face) and not cyberbullying (i.e., online bullying). However, there is significant overlap between the experiences of traditional and cyberbullying. Being bullied online is quite a reliable signal that a child is also bullied in other ways (Przybylski & Bowes, 2017). In fact, in a survey of over 2,700 UK adolescents, only 1% of adolescents were victims of online bullying alone with no traditional bullying (Wolke et al., 2017). Across countries, cyberbullying is still a less frequent form of harassment compared to traditional bullying with a prevalence of 16% for cyber-perpetration and 15% for cyber-victimization (Modecki et al., 2014).

Mental health problems associated with bullying victimization and perpetration – evidence from longitudinal studies

Bullying victimization is a stressful event which triggers immediate adjustment responses, such as signs of psychological distress (e.g., being tearful, irritable, loosing motivation, presenting sleep problems) and social problems (i.e., loneliness, isolation, poor life satisfaction) (Arseneault, 2018; Moore et al., 2017). While some of these reactions may be temporary, other symptoms of psychological distress associated with psychopathology may persist, at least in the short-term. Convincing evidence coming from longitudinal studies with causal designs (including a systematic review of these studies) suggests that as a group, youth who experience frequent bullying victimization are more likely to report anxiety, depression, suicidal ideation and self-harm concurrently and within 1 or 2 years since the reports of the bullying victimization event(s) compared to their peers who are not bullied (Arseneault et al., 2008; Kretschmer et al., 2018; Schoeler et al., 2018; Silberg et al., 2016; Singham et al., 2017). These associations have been explained only partially by genetic or family factors or pre-existent symptoms of mental health problems.

Not only children who are bullied, but also those who bully others are at risk of psychosocial maladjustment. Emerging evidence suggests that, as a group, youth who bully others, irrespective of whether it happened during childhood or adolescence, are more likely to show increased likelihood of later use of tobacco, alcohol, cannabis and hard drugs as well as general substance use (Vrijen et al., 2021). Moreover, bullying perpetrators have increased likelihood of depression, criminal offending and antisocial behaviour (Farrington, 2012; Ttofi et al., 2012; Ganesan et al., 2021).

Fewer studies have looked into the later outcomes of youth who are both perpetrators and targets of bullying (bully-victims). Youth in this group face the most significant challenges of all those involved in bullying. They are more likely to present higher symptoms of psychotic experiences, depression, anxiety and panic disorders, anorexia and later tobacco use (Copeland et al., 2013, 2015; Lereya et al., 2015; Vrijen et al., 2021).

Factors associated with youth’s involvement in bullying

Bullying involvement is not a random event. Individual and contextual factors increase youth’s likelihood of being the target, the perpetrator of bullying or both. Symptoms of mental health problems are not only outcomes of bullying involvement; they may also precede it. Pre-existing externalizing symptoms (e.g., aggression, hyperactivity, antisocial behaviour) have been associated both with subsequent bullying victimization and perpetration (Álvarez-García et al., 2015; Jansen et al., 2011; Reijntjes et al., 2011; Schoeler et al., 2019). Furthermore, pre-existing internalizing symptoms (e.g., depression, anxiety, social withdrawal) have been predominantly associated with increased likelihood of bullying victimization (Reijntjes et al., 2010; Schoeler et al., 2019).

For the majority of the other individual factors (described below), we do not have sufficient evidence yet to clarify if they function as precursors, outcomes of bullying involvement or both. Regarding social cognition, youth who are involved in bullying are more likely to present negative thoughts, beliefs, and attitudes about themselves (e.g., low self-esteem, self-blame) and more negative perceptions of peers and negative interpretation of social cues (e.g., other’s intentions and expectations) (Cook et al., 2010; Kellij et al., 2022). Moreover, youth who bully and bully-victims have low levels of affective empathy (i.e., ability to feel/share the emotions of others) and cognitive empathy (i.e., understanding the emotions of others) (Zych, Ttofi, et al., 2019). Youth who are bullied tend to have similar abilities to empathize as their peers who are not bullied (Zych, Ttofi, et al., 2019; Kellij et al., 2022). On the other end, high levels of self-oriented personal competencies (e.g., high self-esteem, social self-concept) were found to protect against bullying victimization, while other-oriented social competencies (e.g., social problem solving skills, agreeableness, affective and cognitive empathy) and good academic performance were found to protect against bullying perpetration. Positive peer interactions were protective against being a bully-victim (Zych, Farrington, et al., 2019).

Regarding peer status, youth who experience bullying victimization are perceived as less popular compared to bullies and uninvolved peers. They tend to be isolated or rejected by peers potentially due to fear that association with them may jeopardise one’s own social position. Youth who bully are perceived as more popular than their victimized and uninvolved peers. Bully-victims are perceived as less popular than bullies and this may be a reflection of the different way in which they use aggression (i.e., mainly in retaliatory circumstances) (Cook et al., 2010; Guy et al., 2019; Nansel et al., 2001).

Among family factors associated with bullying, studies have consistently showed that children exposed to parental neglect, abuse and maltreatment have an increased likelihood of bullying involvement either as victim or perpetrator, with stronger effects for those who are both the target and perpetrator of bullying (Lereya et al., 2013; Nocentini et al., 2019, Bowes et al., 2009). On the other hand, maternal warmth was found to be protective against behavioural problems for youth who experienced bullying victimization (Bowes et al., 2010).

The role of other contextual factors beyond the family, i.e., school‐ or community‐level factors has been less studied. For instance, higher levels of classrooms status hierarchy (i.e., classes where only few students are perceived as popular by their peers) were associated with higher levels of concurrent and future bullying perpetration (Garandeau, C. F. et al., 2014). Moreover, larger school size was associated with bullying victimization (Bowes et al., 2009), while a positive school climate protected against it (Zych, Farrington, et al., 2019). At community level, problems with neighbours, disorder and safety in the neighbourhood were linked to bullying involvement (Bowes et al., 2009; Zych, Farrington, et al., 2019).

Whole-school interventions to reduce and prevent bullying

School-based anti-bullying interventions and programmes are somewhat effective in reducing bullying involvement. A comprehensive synthesis of evidence on the effectiveness of anti-bullying interventions and programmes indicates that, on average and when compared with schools’ usual practice, these efforts decrease bullying perpetration by 19-20% and bullying victimization by 15-16% (Gaffney et al., 2019). These interventions seem to work better for younger than older school students (Salmivalli et al., 2021). Many anti-bullying programmes have a whole-school approach, i.e., they involve multiple components (e.g., policies, culture, and classroom practice) that interact with each other and with the context to modify the school ethos and promote social and emotional learning. The most researched and well-known whole-school programmes for bullying prevention are the Olweus Bullying Prevention Program (OBPP) and KiVa programme. Both programmes aim to improve the school climate and have as primary objectives the reduction of bullying victimization and perpetration at school level. They combine universal preventive actions (i.e., those addressed to all students and the whole-school community) with targeted actions (i.e., those specifically addressed to new or ongoing incidents of bullying).

Olweus Bullying Prevention Program (OBPP)

The OBPP programme was developed in Norway in the mid-1980s and is grounded in research on the development and modification of aggressive behaviour. The programme aims to restructure the social environment of the school (mainly through the activity of the school personnel) in order to reduce opportunities and rewards for bullying and build a sense of community (Olweus et al., 2021). The whole-school components include a tailored school plan to implement the OBPP, introduction of school rules against bullying, increased adult supervision of school areas that are frequently the setting for bullying (i.e., the playground, cafeteria and bathrooms) and a school kick-off event to launch the programme. At the classroom level, for students, the programme includes regular class discussions and activities designed to reinforce rules and anti-bullying values and norms. The programme also involves parents by holding meetings to help them understand problems associated with bullying and ways to address them. The targeted actions to address cases of bullying rely on applying consistent nonphysical, nonhostile sanctions when anti-bullying rules are broken. The OBPP is addressed to students aged 5-15 years old and has also been adapted for older students (Olweus et al., 2021; EMCDDA, 2018). The evaluations studies of the programme in Norway, US and its implementation in Lithuania showed reductions in bullying perpetration and victimization (Olweus et al., 2020; Olweus & Limber, 2010; Sullivan et al., 2021).

KiVa programme

The KiVa programme was developed in Finland in 2006. It focuses on influencing bystanders’ reactions to bullying, so that they are more likely to support the victimized peers than encourage the bully (Salmivalli et al., 1996). The universal components include posters, online games, detailed materials and events for students, teachers and parents, and high visibility vests for recess supervisors. The classroom lessons for students cover the roles of all the group members (e.g., bystanders, assistants) in maintaining bullying and promoting strategies to support the victimized student. The targeted actions to address cases of bullying involve separate meetings and systematic follow-ups with the victim and the bully. For the victimized student, a support group comprising classmates can be established. For the perpetrator, the school staff can choose a confronting approach (condemning the bullying, holding the bully fully responsible for the harm caused and implementing sanctions such as serious talks and informing the parents) or non-confronting approach (arousing bullies’ empathy for their victim by explaining that the situation is painful for the victimized peer). The programme has three developmentally appropriate versions for ages 7–9 years, 10 –12 years, and 13 –15 years (EMCDDA, 2020; Yun & Salmivalli, 2021). The KiVa programme has shown to be effective in reducing bullying and victimization in evaluation studies using cluster randomized controlled trial (RCT) design in Finland (Kärnä et al., 2011, 2013), Italy (Nocentini & Menesini, 2016) and Netherlands (Huitsing et al., 2020). KiVa has been rolled out nationwide in Finland and has been used internationally in more than 20 countries.

Learning Together intervention

More recently, in 2011, the Learning Together intervention aimed at reducing bullying and aggressive behaviours was developed in the UK (Bonell et al., 2018). The core principle of this whole-school intervention is to involve students in efforts to modify the school environment using restorative practice and by developing their social and emotional skills. The restorative practice aims to prevent or resolve conflicts between students or between staff and students. It focuses on repairing relationships rather than just punishing bad behaviour. It involves responding to conflict by understanding the causes of conflict, improving relationships, and re-integrating offenders back into the school community. Universal actions consist of modifying the overall school policies and systems and ensuring students have a say in this process (e.g., action groups in which staff and students work together). At the classroom level, social and emotional education is promoted through lessons on how to manage emotions and relationships. Targeted actions to address incidents of bullying are based on restorative practice. This may take the form of a staff member leading a facilitated meeting between a bully and their victim. The victim is given the opportunity to describe the impact of the bullying, the bully is encouraged to acknowledge this harm and their responsibility for it, and the facilitator works with the two parties to enable healing in their relationship and the prevention of further problems. The effectiveness of the intervention over three years was investigated in a cluster RCT among youth (aged 12-15 years) in the UK. It showed small but significant effects on reducing bullying victimization, but no effect on aggression (Bonell et al., 2018).

 

Risk factors and protective factors for, and outcomes of bullying involvement – disentangling correlation from causation

With the exception of some mental health outcomes described above (Schoeler et al., 2018), we lack robust evidence from longitudinal studies and quasi-experimental designs (e.g., discordant twin design, propensity score matching) regarding outcomes of, and risk and protective factors for, exposure to bullying involvement. For instance, regarding outcomes, we have indications that bullying involvement is associated with physical ill health (Schacter, 2021), low academic achievement (Kochenderfer-Ladd et al., 2021), dating violence (Zych et al., 2021), psychosis, eating disorders (Copeland et al., 2015), and mental health comorbidities (Oncioiu et al., 2021). Moreover, regarding risk and protective factors, some evidence exists that parents’ psychopathology (Nocentini et al., 2019), sibling bullying (Wolke & Skew, 2012), living in a separated family (Brendgen et al., 2016; Oncioiu et al., 2020), and low socio-economic status (Biswas et al., 2020; Bowes et al., 2013) are associated with bullying victimization, while high self-esteem or positive home environment, parental involvement and support were protective against bullying involvement (Zych, Farrington, et al., 2019). However, in the majority of these studies, we do not know if the outcomes actually precede bullying involvement (i.e., reverse causality) and/or if the observed associations can be explained by confounding factors (e.g., genetic/familial risk factors, individual characteristics). Therefore, we cannot draw any conclusions yet about the nature of these associations (i.e., correlational or causal).

Resilience

As pointed out by a recent systematic review of meta-analyses on protective factors against bullying, with few exceptions, most studies in the literature do not distinguish between factors that are associated with minimal bullying involvement (i.e., direct protective factors) and factors that buffer against negative outcomes for youth involved in bullying (i.e., risk-based protective factors/factors that promote resilience) (Zych, Farrington, et al., 2019). Among the exceptions, one systematic review looked at factors that promote resilience following bullying involvement. It found that good performance at school and good social skills, coming from a stable (undisrupted) family, being attached to parents, and having prosocial friends, were factors that interrupted the continuity from school bullying (both perpetration and victimization) to later behavioural and emotional problems (Ttofi et al., 2014). Future research should focus on understanding the individual and contextual factors that enhance resilience following bullying involvement while acknowledging that resilience is not a quality within individuals, rather it depends on the access to and use of resources needed to support healthy relationships, mental health and well-being (Ungar & Theron, 2020).

Mechanisms linking bullying involvement with adverse outcomes

Evidence is scarce about the mechanisms through which bullying involvement leads to adverse mental and physical health outcomes. So far, some of the mechanisms explaining the association between childhood maltreatment and mental health (McLaughlin et al., 2019) have been investigated in relation to bullying. For instance, at a biological level, there are indications that bullying victimization is associated with dysfunction of the stress response system (e.g., dysregulation of cortisol levels which diminishes a person’s ability to cope with stress) (Ouellet-Morin et al., 2011;Vaillancourt, Duku, et al., 2008) and with systemic inflammation (Baldwin et al., 2018; Copeland et al., 2014). Moreover, recent evidence showed that dysregulated levels of cortisol were one of the mechanisms explaining partially the association between bullying victimization and depressive symptoms (Iob et al., 2021).

Similarly, at a psychological level, bullying seems to influence emotional and cognitive processing which are known mechanisms that explain the association of early childhood adversity with psychopathology (McLaughlin et al., 2019). For instance, a recent study found that different types of emotional and cognitive regulation difficulties serve as a pathway from peer victimization to depressive symptoms (e.g., behavioural regulation difficulties, such as the tendency to act impulsively when emotionally dysregulated) and anxiety (e.g., cognitive regulation difficulties, such as rumination) (Adrian et al., 2019).

Mechanisms of anti-bullying interventions

The mechanisms of change through which anti-bullying programmes work remain largely unknown. Nevertheless, we are starting to understand which intervention components are effective in reducing bullying perpetration and victimization. For instance, a systematic review found that interventions including information for parents and informal peer involvement as part of the intervention activities (e.g., use of in-class, or group-based discussions related to bullying experiences and attitudes) resulted in larger reductions in both bullying perpetration and victimization compared to interventions which did not include the respective components (Gaffney et al., 2021). Moreover, interventions which included several other components (e.g., whole-school approach, anti-bullying policies, classroom rules, work with victims) showed greater reduction in bullying perpetration compared to those that did not include these components. However, we still need to understand if anti-bullying programmes are also effective in reducing the burden of mental health problems associated with bullying victimization and perpetration. A recent systematic review and meta-analysis found that anti-bullying interventions have a small impact in reducing overall internalizing symptoms, anxiety and depression. This study also suggested that one promising component in reducing internalizing problems may be the involvement of peers in anti-bullying efforts (e.g., as mentors, mediators or through bystander training) (Guzman-Holst et al., 2022).

Furthermore, we do not know what works in terms of anti-bullying prevention for youth with physical and intellectual disabilities, special educational needs, attention deficit hyperactivity disorder or autism spectrum disorders, those of minority ethnic groups or LGBTQ+ youth. For instance, one systematic review on stigma-based anti-bullying interventions (Earnshaw et al., 2018) and one focusing on anti-bullying interventions for students with disability (Houchins et al., 2016) concluded that so far these interventions are generally not theory-based and lack rigorous and systematic evaluations.

Finally, to adapt interventions to different school/country contexts, it is essential to gain a better understanding of the contextual and systemic factors that influence the implementation of anti-bullying interventions and the uptake of their specific components (e.g., Warren et al., 2020).

The interplay between individual, contextual and systemic factors

Bullying is more than the relationship between the perpetrator and the target of bullying. This relationship is embedded in macro-level, micro-level and locally constructed norms and categories. For instance, a qualitative study documented that in a fat-phobic society, in the same classroom, an overweight girl was perceived as abnormal and ugly and was bullied due to her physical appearance, while an overweight boy was perceived as physically strong and assertive. He belonged to the group of popular boys and was bullying his classmates who were overweight (Thornberg, 2018). Moreover, another qualitative study suggested that bullying victimization can also happen in the absence of a leading perpetrator (i.e., collective bullying becomes a binding ritual for an entire classroom that ostracises one pupil) (Hakim, 2020). More mixed-method research (i.e., use of qualitative and quantitative methods in the same study population) is needed to understand how “peer cultures, social hierarchies, power dynamics, cultural norms and intersectionality lead to bullying” (Thornberg, 2018).

In terms of whole-school anti-bullying interventions, UK researchers are currently studying if the effects of the KiVa programme observed in some countries (e.g., Finland, Netherlands) can transfer over to the UK which has a very different education system (e.g., in terms of curriculum, teachers training and salary, size of the class, social inequalities). An effectiveness cluster randomized control trial (The Stand Together trial) is being carried out to investigate if the KiVa programme over one academic year is more effective in reducing bullying victimisation among pupils aged 7-11 years than usual practice (Clarkson et al., 2022). The results of this trial will inform if the KiVa programme can be rolled out across the UK.

In terms of targeted prevention, it is crucial to understand the modifiable risk factors for severe and chronic cases of bullying perpetration and victimization. These cases are usually not solved by school-based interventions that successfully reduce overall rates of bullying and victimization (Kaufman et al., 2018). Moreover, youth who continue to be victimized in schools where interventions are successful in creating safer environments may experience worse psychosocial problems than prior to the intervention (i.e., ‘healthy context paradox’) (Garandeau & Salmivalli, 2019). It has been suggested that in schools/classrooms where bullying rates drop, the very few victimized students may feel worse as they blame themselves for continuing to be bullied or have fewer opportunities to befriend other children in their situation (e.g., children who are bullied) (Salmivalli, 2021). Efforts to understand the ‘healthy context paradox’ are essential to develop targeted interventions which can effectively reduce chronic bullying and the socio-emotional challenges associated with it.

In terms of innovative designs, natural experiments and virtual reality have the potential to move forward the research in the field of bullying. The COVID-19 pandemic can be conceptualised as a natural experiment that allows us to understand how the rates of bullying are affected by systemic changes within the education system (e.g., school closures and re-openings, increased supervision, reduced class sizes, and blended learning) which were implemented to reduce the spread of the virus in many countries. Preliminary results suggest that rates of traditional bullying decreased during the COVID-19 pandemic when compared to pre-pandemic levels (Soneson et al., 2022; Vaillancourt et al., 2021). However, it is important to continue to monitor the levels of bullying once all the COVID-19 restrictions have been lifted.

Virtual reality has a unique potential for studying bullying and for clinical/therapeutic work with those involved in bullying. Virtual reality technology combines in a safe way laboratory conditions (i.e., precise presentation and control of stimuli) with an immersive real-life experience (i.e., psychological sensation of being there). Moreover, it allows researchers to witness participants’ experience first-hand rather than to rely on retrospective data collection or subjective reports (Barreda-Ángeles et al., 2021; Valmaggia et al., 2016). For example, via an avatar, virtual reality enables researchers to study participants’ immediate reactions to witnessing/experiencing different bullying scenarios. It also allows clinicians to train individuals in perspective-taking skills by assuming the role of the youth exposed to victimization in an environment that feels realistic. Currently, researchers are using virtual reality to investigating if youth with existing mental health difficulties may display greater sensitivity to negative peer interactions (low-level verbal bullying) (oRANGE, 2021). For youth who bully others or who have been bullied, this technology could open the doors for tailored individual interventions during actual social interactions with peers in an immersive environment. In this way the clinician can safely manipulate (e.g., adapt, repeat, stop) the triggers that elicit bullying behaviours or distress, and help the youth to learn to better manage their reactions (Alsem et al., 2021; Ingram et al., 2019).

Free, private and confidential support services for youth in the UK as well as resources on mental health and bullying:

Childline: phone, email, 1-2-1 chat for youth under 19 years old in the UK

Shout 85258: 24/7 text messaging support service for anyone in the UK.

The Samaritans: phone, email, in-person, letter support service in English and Welsh.

Anti-bullying Alliance – coalition of organisations and individuals, working together to stop bullying; useful resources for youth, parents, teachers and free CPD-certified anti-bullying online training for anyone working with youth.

Respect Me – Scotland’s Anti-Bullying Service.

Always Take Action – a collection of young people’s testimonies along with research results on bullying by the World Anti-Bullying Forum.

Adrian, M., Jenness, J. L., Kuehn, K. S., Smith, M. R., & McLaughlin, K. A. (2019). Emotion regulation processes linking peer victimization to anxiety and depression symptoms in adolescence. Development and Psychopathology, 31(3), 999–1009. https://doi.org/10.1017/S0954579419000543

Alsem, S. C., van Dijk, A., Verhulp, E. E., & De Castro, B. O. (2021). Using virtual reality to treat aggressive behavior problems in children: A feasibility study. Clinical Child Psychology and Psychiatry, 26(4), 1062–1075. https://doi.org/10.1177/13591045211026160

Álvarez-García, D., García, T., & Núñez, J. C. (2015). Predictors of school bullying perpetration in adolescence: A systematic review. Aggression and Violent Behavior, 23, 126–136. https://doi.org/10.1016/j.avb.2015.05.007

Armitage, J. M., Morneau-Vaillancourt, G., Pingault, J.-B., Andlauer, T. F. M., Paquin, S., Langevin, S., Brendgen, M., Dionne, G., Séguin, J., Rouleau, G., Vitaro, F., Ouellet-Morin, I., & Boivin, M. (2022). A multi-informant and multi-polygenic approach to understanding predictors of peer victimisation in childhood and adolescence. JCPP Advances, 2(1), e12063. https://doi.org/10.1002/jcv2.12063

Arseneault, L. (2018). Annual Research Review: The persistent and pervasive impact of being bullied in childhood and adolescence: implications for policy and practice. Journal of Child Psychology and Psychiatry, and Allied Disciplines, 59(4), 405–421. https://doi.org/10.1111/jcpp.12841

Arseneault, L., Milne, B. J., Taylor, A., Adams, F., Delgado, K., Caspi, A., & Moffitt, T. E. (2008). Being bullied as an environmentally mediated contributing factor to children’s internalizing problems: A study of twins discordant for victimization. Archives of Pediatrics & Adolescent Medicine, 162(2), 145–150. https://doi.org/10.1001/archpediatrics.2007.53

Baldwin, J. R., Arseneault, L., Caspi, A., Fisher, H. L., Moffitt, T. E., Odgers, C. L., Pariante, C., Ambler, A., Dove, R., Kepa, A., Matthews, T., Menard, A., Sugden, K., Williams, B., & Danese, A. (2018). Childhood victimization and inflammation in young adulthood: A genetically sensitive cohort study. Brain, Behavior, and Immunity, 67, 211–217. https://doi.org/10.1016/j.bbi.2017.08.025

Barreda-Ángeles, M., Serra-Blasco, M., Trepat, E., Pereda-Baños, A., Pàmias, M., Palao, D., Goldberg, X., & Cardoner, N. (2021). Development and experimental validation of a dataset of 360°-videos for facilitating school-based bullying prevention programs. Computers & Education, 161, 104065. https://doi.org/10.1016/j.compedu.2020.104065

Biswas, T., Scott, J. G., Munir, K., Thomas, H. J., Huda, M. M., Hasan, M. M., Vries, T. D. de, Baxter, J., & Mamun, A. A. (2020). Global variation in the prevalence of bullying victimisation amongst adolescents: Role of peer and parental supports. EClinicalMedicine, 20. https://doi.org/10.1016/j.eclinm.2020.100276

Bonell, C., Allen, E., Warren, E., McGowan, J., Bevilacqua, L., Jamal, F., Legood, R., Wiggins, M., Opondo, C., Mathiot, A., Sturgess, J., Fletcher, A., Sadique, Z., Elbourne, D., Christie, D., Bond, L., Scott, S., & Viner, R. M. (2018). Effects of the Learning Together intervention on bullying and aggression in English secondary schools (INCLUSIVE): A cluster randomised controlled trial. The Lancet, 392(10163), 2452–2464. https://doi.org/10.1016/S0140-6736(18)31782-3

Bowes, L., Arseneault, L., Maughan, B., Taylor, A., Caspi, A., & Moffitt, T. E. (2009). School, neighborhood, and family factors are associated with children’s bullying involvement: A nationally representative longitudinal study. Journal of the American Academy of Child and Adolescent Psychiatry, 48(5), 545–553. https://doi.org/10.1097/CHI.0b013e31819cb017

Bowes, L., Maughan, B., Ball, H., Shakoor, S., Ouellet-Morin, I., Caspi, A., Moffitt, T. E., & Arseneault, L. (2013). Chronic bullying victimization across school transitions: The role of genetic and environmental influences. Development and Psychopathology, 25(2). https://doi.org/10.1017/S0954579412001095

Bowes, L., Maughan, B., Caspi, A., Moffitt, T. E., & Arseneault, L. (2010). Families promote emotional and behavioural resilience to bullying: Evidence of an environmental effect. Journal of Child Psychology and Psychiatry, and Allied Disciplines, 51(7), 809–817. https://doi.org/10.1111/j.1469-7610.2010.02216.x

Brendgen, M., Girard, A., Vitaro, F., Dionne, G., & Boivin, M. (2016). Personal and familial predictors of peer victimization trajectories from primary to secondary school. Developmental Psychology, 52(7), 1103–1114. https://doi.org/10.1037/dev0000107

Clarkson, S., Bowes, L., Coulman, E., Broome, M. R., Cannings-John, R., Charles, J. M., Edwards, R. T., Ford, T., Hastings, R. P., Hayes, R., Patterson, P., Segrott, J., Townson, J., Watkins, R., Badger, J., & Hutchings, J. (2022). The UK Stand Together trial: Protocol for a multicentre cluster randomised controlled trial to evaluate the effectiveness and cost-effectiveness of KiVa to reduce bullying in primary schools. BMC Public Health, 22, 608. https://doi.org/10.1186/s12889-022-12642-x

Cook, C. R., Williams, K. R., Guerra, N. G., Kim, T. E., & Sadek, S. (2010). Predictors of bullying and victimization in childhood and adolescence: A meta-analytic investigation. School Psychology Quarterly, 25(2), 65–83. https://doi.org/10.1037/a0020149

Copeland, W. E., Bulik, C. M., Zucker, N., Wolke, D., Lereya, S. T., & Costello, E. J. (2015). Does childhood bullying predict eating disorder symptoms? A prospective, longitudinal analysis. International Journal of Eating Disorders, 48(8), 1141–1149. https://doi.org/10.1002/eat.22459

Copeland, W. E., Wolke, D., Angold, A., & Costello, E. J. (2013). Adult Psychiatric and Suicide Outcomes of Bullying and Being Bullied by Peers in Childhood and Adolescence. JAMA Psychiatry (Chicago, Ill.), 70(4), 419–426. https://doi.org/10.1001/jamapsychiatry.2013.504

Copeland, W. E., Wolke, D., Lereya, S. T., Shanahan, L., Worthman, C., & Costello, E. J. (2014). Childhood bullying involvement predicts low-grade systemic inflammation into adulthood. Proceedings of the National Academy of Sciences of the United States of America, 111(21), 7570–7575. https://doi.org/10.1073/pnas.1323641111

Department of Education. (2019). Bullying in England, April 2013 to March 2018 (Ad-hoc Notice). https://www.gov.uk/government/publications/bullying-in-england-april-2013-to-march-2018

Earnshaw, V. A., Reisner, S. L., Menino, D., Poteat, V. P., Bogart, L. M., Barnes, T. N., & Schuster, M. A. (2018). Stigma-Based Bullying Interventions: A Systematic Review. Developmental Review: DR, 48, 178–200. https://doi.org/10.1016/j.dr.2018.02.001

EMCDDA, The European Monitoring Centre for Drugs and Drug Addiction. (2018). Olweus Bullying Prevention Programme—A school-wide programme designed to prevent bullying amongst children. https://www.emcdda.europa.eu/best-practice/xchange/olweus-bullying-prevention-programme-school-wide-programme-designed-prevent-bullying-amongst-children_en#impexp

EMCDDA, The European Monitoring Centre for Drugs and Drug Addiction. (2020). KiVa (Anti-bullying programme)—Combined universal and indicated type of an anti-bullying programme for school children. https://www.emcdda.europa.eu/best-practice/xchange/kiva-anti-bullying-programme-combined-universal-and-indicated-type-anti-bullying-programme-school-children_en

Farrington, D. P. (2012). School bullying, depression and offending behavior later in life: An updated systematic review of longitudinal studies. BRÅ, National Council for Crime Prevention.

Finkelhor, D., Ormrod, R. K., & Turner, H. A. (2007). Poly-victimization: A neglected component in child victimization. Child Abuse & Neglect, 31(1), 7–26. https://doi.org/10.1016/j.chiabu.2006.06.008

Gaffney, H., Ttofi, M. M., & Farrington, D. P. (2019). Evaluating the effectiveness of school-bullying prevention programs: An updated meta-analytical review. Aggression and Violent Behavior, 45, 111–133. https://doi.org/10.1016/j.avb.2018.07.001

Gaffney, H., Ttofi, M. M., & Farrington, D. P. (2021). What works in anti-bullying programs? Analysis of effective intervention components. Journal of School Psychology, 85, 37–56. https://doi.org/10.1016/j.jsp.2020.12.002

Ganesan, K., Shakoor, S., Wertz, J., Agnew-Blais, J., Bowes, L., Jaffee, S. R., Matthews, T., & Arseneault, L. (2021). Bullying behaviours and other conduct problems: Longitudinal investigation of their independent associations with risk factors and later outcomes. Social Psychiatry and Psychiatric Epidemiology, 56(11), 2041–2052. https://doi.org/10.1007/s00127-021-02062-4

Garandeau, C. F., & Salmivalli, C. (2019). Can Healthier Contexts Be Harmful? A New Perspective on the Plight of Victims of Bullying. Child Development Perspectives, 13(3), 147–152. https://doi.org/10.1111/cdep.12331

Garandeau, C. F., Lee, Ihno A., & Salmivalli, Christina. (2014). Inequality Matters: Classroom Status Hierarchy and Adolescents’ Bullying. Journal of Youth and Adolescence, 43, 1123null. https://doi.org/10.1007/s10964-013-0040-4

Gladden, R., Vivolo-Kantor, A., Hamburger, M., & Lumpkin, C. (2014). Bullying Surveillance Among Youths: Uniform Definitions for Public Health and Recommended Data Elements, Version 1.0. https://www.cdc.gov/violenceprevention/pdf/bullying-definitions-final-a.pdf

Green, J. G., Felix, E. D., Sharkey, J. D., Furlong, M. J., & Kras, J. E. (2013). Identifying bully victims: Definitional versus behavioral approaches. Psychological Assessment, 25(2), 651–657. https://doi.org/10.1037/a0031248

Guy, A., Lee, K., & Wolke, D. (2019). Comparisons Between Adolescent Bullies, Victims, and Bully-Victims on Perceived Popularity, Social Impact, and Social Preference. Frontiers in Psychiatry, 10. https://www.frontiersin.org/article/10.3389/fpsyt.2019.00868

Guzman-Holst, C., Zaneva, M., Chessell, C., Creswell, C., & Bowes, L. (2022). Research Review: Do antibullying interventions reduce internalizing symptoms? A systematic review, meta-analysis, and meta-regression exploring intervention components, moderators, and mechanisms. Journal of Child Psychology and Psychiatry, and Allied Disciplines. https://doi.org/10.1111/jcpp.13620

Hakim, E. (2020). You’ve got the disease: How disgust in child culture shapes school bullying. Ethnography and Education. https://doi.org/10.1080/17457823.2020.1864655

Houchins, D. E., Oakes, W. P., & Johnson, Z. G. (2016). Bullying and Students With Disabilities: A Systematic Literature Review of Intervention Studies. Remedial and Special Education, 37(5), 259–273. https://doi.org/10.1177/0741932516648678

Huitsing, G., Lodder, G. M. A., Browne, W. J., Oldenburg, B., Van der Ploeg, R., & Veenstra, R. (2020). A Large-Scale Replication of the Effectiveness of the KiVa Antibullying Program: A Randomized Controlled Trial in the Netherlands. Prevention Science: The Official Journal of the Society for Prevention Research, 21(5), 627–638. https://doi.org/10.1007/s11121-020-01116-4

Ingram, K. M., Espelage, D. L., Merrin, G. J., Valido, A., Heinhorst, J., & Joyce, M. (2019). Evaluation of a virtual reality enhanced bullying prevention curriculum pilot trial. Journal of Adolescence, 71, 72–83. https://doi.org/10.1016/j.adolescence.2018.12.006

Iob, E., Baldwin, J. R., Plomin, R., & Steptoe, A. (2021). Adverse childhood experiences, daytime salivary cortisol, and depressive symptoms in early adulthood: A longitudinal genetically informed twin study. Translational Psychiatry, 11(1), 1–10. https://doi.org/10.1038/s41398-021-01538-w

Jansen, D. E., Veenstra, R., Ormel, J., Verhulst, F. C., & Reijneveld, S. A. (2011). Early risk factors for being a bully, victim, or bully/victim in late elementary and early secondary education. The longitudinal TRAILS study. BMC Public Health, 11, 440. https://doi.org/10.1186/1471-2458-11-440

Kann, L. (2016). Sexual Identity, Sex of Sexual Contacts, and Health-Related Behaviors Among Students in Grades 9–12—United States and Selected Sites, 2015. MMWR. Surveillance Summaries, 65. https://doi.org/10.15585/mmwr.ss6509a1

Kärnä, A., Voeten, M., Little, T. D., Alanen, E., Poskiparta, E., & Salmivalli, C. (2013). Effectiveness of the KiVa Antibullying Program: Grades 1–3 and 7–9. Journal of Educational Psychology, 105(2), 535–551. https://doi.org/10.1037/a0030417

Kärnä, A., Voeten, M., Little, T. D., Poskiparta, E., Kaljonen, A., & Salmivalli, C. (2011). A large-scale evaluation of the KiVa antibullying program: Grades 4-6. Child Development, 82(1), 311–330. https://doi.org/10.1111/j.1467-8624.2010.01557.x

Kaufman, T. M. L., Kretschmer, T., Huitsing, G., & Veenstra, R. (2018). Why Does a Universal Anti-Bullying Program Not Help All Children? Explaining Persistent Victimization During an Intervention. Prevention Science, 19(6), 822–832. https://doi.org/10.1007/s11121-018-0906-5

Kellij, S., Lodder, G. M. A., van den Bedem, N., Güroğlu, B., & Veenstra, R. (2022). The Social Cognitions of Victims of Bullying: A Systematic Review. Adolescent Research Review. https://doi.org/10.1007/s40894-022-00183-8

Kochenderfer-Ladd, B., Ladd, G. W., & Thibault, S. A. (2021). School Bullying and Peer Victimization-Its Role in Students’ Academic Achievement. In The Wiley Blackwell Handbook of Bullying (pp. 619–638). John Wiley & Sons, Ltd. https://doi.org/10.1002/9781118482650.ch34

Kretschmer, T., Tropf, F. C., & Niezink, N. M. D. (2018). Causality and Pleiotropy in the Association Between Bullying Victimization in Adolescence and Depressive Episodes in Adulthood. Twin Research and Human Genetics: The Official Journal of the International Society for Twin Studies, 21(1), 33–41. https://doi.org/10.1017/thg.2017.71

Lereya, S. T., Copeland, W. E., Zammit, S., & Wolke, D. (2015). Bully/victims: A longitudinal, population-based cohort study of their mental health. European Child & Adolescent Psychiatry, 24(12), 1461–1471. https://doi.org/10.1007/s00787-015-0705-5

Lereya, S. T., Samara, M., & Wolke, D. (2013). Parenting behavior and the risk of becoming a victim and a bully/victim: A meta-analysis study. Child Abuse & Neglect, 37(12), 1091–1108. https://doi.org/10.1016/j.chiabu.2013.03.001

McLaughlin, K. A., DeCross, S. N., Jovanovic, T., & Tottenham, N. (2019). Mechanisms linking childhood adversity with psychopathology: Learning as an intervention target. Behaviour Research and Therapy, 118, 101–109. https://doi.org/10.1016/j.brat.2019.04.008

Modecki, K. L., Minchin, J., Harbaugh, A. G., Guerra, N. G., & Runions, K. C. (2014). Bullying prevalence across contexts: A meta-analysis measuring cyber and traditional bullying. The Journal of Adolescent Health: Official Publication of the Society for Adolescent Medicine, 55(5), 602–611. https://doi.org/10.1016/j.jadohealth.2014.06.007

Moore, S. E., Norman, R. E., Suetani, S., Thomas, H. J., Sly, P. D., & Scott, J. G. (2017). Consequences of bullying victimization in childhood and adolescence: A systematic review and meta-analysis. World Journal of Psychiatry, 7(1), 60–76. https://doi.org/10.5498/wjp.v7.i1.60

Nansel, T. R., Overpeck, M., Pilla, R. S., Ruan, W. J., Simons-Morton, B., & Scheidt, P. (2001). Bullying Behaviors Among US Youth Prevalence and Association With Psychosocial Adjustment. JAMA, 285(16), 2094–2100. https://doi.org/10.1001/jama.285.16.2094

Nocentini, A., Fiorentini, G., Di Paola, L., & Menesini, E. (2019). Parents, family characteristics and bullying behavior: A systematic review. Aggression and Violent Behavior, 45, 41–50. https://doi.org/10.1016/j.avb.2018.07.010

Nocentini, A., & Menesini, E. (2016). KiVa Anti-Bullying Program in Italy: Evidence of Effectiveness in a Randomized Control Trial. Prevention Science: The Official Journal of the Society for Prevention Research, 17(8), 1012–1023. https://doi.org/10.1007/s11121-016-0690-z

Olweus Bullying Prevention Programme—A school-wide programme designed to prevent bullying amongst children | www.emcdda.europa.eu. (n.d.). Retrieved February 27, 2022, from https://www.emcdda.europa.eu/best-practice/xchange/olweus-bullying-prevention-programme-school-wide-programme-designed-prevent-bullying-amongst-children_en

Olweus, D. (1983). The Olweus Bully/Victim Questionnaire. Mimeo. Bergen, Norway. Research Centre for Health Promotion (HEMIL), University of Bergen.

Olweus, D. (2013). School Bullying: Development and Some Important Challenges. Annual Review of Clinical Psychology, 9(1), 751–780. https://doi.org/10.1146/annurev-clinpsy-050212-185516

Olweus, D., & Limber, S. P. (2010). Bullying in School: Evaluation and Dissemination of the Olweus Bullying Prevention Program. American Journal of Orthopsychiatry, 80(1), 124–134. https://doi.org/10.1111/j.1939-0025.2010.01015.x

Olweus, D., & Limber, S. P. (2019). The Olweus Bullying Prevention Program (OBPP). In Making an Impact on School Bullying. Routledge.

Olweus, D., Limber, S. P., Riese, J., Urbanski, J., Solberg, M. E., & Breivik, K. (2021). The Olweus Bullying Prevention Program (OBPP). In The Wiley Blackwell Handbook of Bullying (pp. 410–429). John Wiley & Sons, Ltd. https://doi.org/10.1002/9781118482650.ch56

Olweus, D., Solberg, M. E., & Breivik, K. (2020). Long-term school-level effects of the Olweus Bullying Prevention Program (OBPP). Scandinavian Journal of Psychology, 61(1), 108–116. https://doi.org/10.1111/sjop.12486

Oncioiu, S. I., Boivin, M., Geoffroy, M.-C., Arseneault, L., Galéra, C., Navarro, M. C., Brendgen, M., Vitaro, F., Tremblay, R. E., Côté, S. M., & Orri, M. (2021). Mental health comorbidities following peer victimization across childhood and adolescence: A 20-year longitudinal study. Psychological Medicine, 1–13. https://doi.org/10.1017/S0033291721003822

Oncioiu, S. I., Orri, M., Boivin, M., Geoffroy, M.-C., Arseneault, L., Brendgen, M., Vitaro, F., Navarro, M. C., Galéra, C., Tremblay, R. E., & Côté, S. M. (2020). Early Childhood Factors Associated With Peer Victimization Trajectories From 6 to 17 Years of Age. Pediatrics, 145(5). https://doi.org/10.1542/peds.2019-2654

oRANGE, Oxford Lab of Risk and Resilience, Genes &. Environment. (2021). Anti-bullying Week—Adolescent Responses to a Bullying Situation. https://www.orangelaboxford.com/anti-bullying-week.html

Ouellet-Morin, I., Danese, A., Bowes, L., Shakoor, S., Ambler, A., Pariante, C. M., Papadopoulos, A. S., Caspi, A., Moffitt, T. E., & Arseneault, L. (2011). A Discordant Monozygotic Twin Design Shows Blunted Cortisol Reactivity Among Bullied Children. Journal of the American Academy of Child and Adolescent Psychiatry, 50(6), 574-582.e3. https://doi.org/10.1016/j.jaac.2011.02.015

Przybylski, A. K., & Bowes, L. (2017). Cyberbullying and adolescent well-being in England: A population-based cross-sectional study. The Lancet. Child & Adolescent Health, 1(1), 19–26. https://doi.org/10.1016/S2352-4642(17)30011-1

Reijntjes, A., Kamphuis, J. H., Prinzie, P., Boelen, P. A., van der Schoot, M., & Telch, M. J. (2011). Prospective linkages between peer victimization and externalizing problems in children: A meta-analysis. Aggressive Behavior, 37(3), 215–222. https://doi.org/10.1002/ab.20374

Reijntjes, A., Kamphuis, J. H., Prinzie, P., & Telch, M. J. (2010). Peer victimization and internalizing problems in children: A meta-analysis of longitudinal studies. Child Abuse & Neglect, 34(4), 244–252. https://doi.org/10.1016/j.chiabu.2009.07.009

Rønning, J. A., Sourander, A., Kumpulainen, K., Tamminen, T., Niemelä, S., Moilanen, I., Helenius, H., Piha, J., & Almqvist, F. (2009). Cross-informant agreement about bullying and victimization among eight-year-olds: Whose information best predicts psychiatric caseness 10-15 years later? Social Psychiatry and Psychiatric Epidemiology, 44(1), 15–22. https://doi.org/10.1007/s00127-008-0395-0

Salmivalli, C. (2021). Challenging bullying cases: Let’s take the challenge (Always Take Action). Friends, World Anti-Bullying Forum. https://worldantibullyingforum.com/uploads/sites/2/2021/06/Anthology-Always-take-action.pdf

Salmivalli, C., Lagerspetz, K., Björkqvist, K., Österman, K., & Kaukiainen, A. (1996). Bullying as a group process: Participant roles and their relations to social status within the group. Aggressive Behavior, 22(1), 1–15. https://doi.org/10.1002/(SICI)1098-2337(1996)22:1<1::AID-AB1>3.0.CO;2-T

Salmivalli, C., Laninga-Wijnen, L., Malamut, S. T., & Garandeau, C. F. (2021). Bullying Prevention in Adolescence: Solutions and New Challenges from the Past Decade. Journal of Research on Adolescence, 31(4), 1023–1046. https://doi.org/10.1111/jora.12688

Schacter, H. L. (2021). Effects of Peer Victimization on Child and Adolescent Physical Health. Pediatrics, 147(1), e2020003434. https://doi.org/10.1542/peds.2020-003434

Schoeler, T., Choi, S. W., Dudbridge, F., Baldwin, J., Duncan, L., Cecil, C. M., Walton, E., Viding, E., McCrory, E., & Pingault, J.-B. (2019). Multi-Polygenic Score Approach to Identifying Individual Vulnerabilities Associated With the Risk of Exposure to Bullying. JAMA Psychiatry. https://doi.org/10.1001/jamapsychiatry.2019.0310

Schoeler, T., Duncan, L., Cecil, C. M., Ploubidis, G. B., & Pingault, J.-B. (2018). Quasi-experimental evidence on short- and long-term consequences of bullying victimization: A meta-analysis. Psychological Bulletin, 144(12), 1229–1246. https://doi.org/10.1037/bul0000171

Sentenac, M., Arnaud, C., Gavin, A., Molcho, M., Gabhainn, S. N., & Godeau, E. (2012). Peer victimization among school-aged children with chronic conditions. Epidemiologic Reviews, 34, 120–128. https://doi.org/10.1093/epirev/mxr024

Shakoor, S., Jaffee, S. R., Andreou, P., Bowes, L., Ambler, A. P., Caspi, A., Moffitt, T. E., & Arseneault, L. (2011). Mothers and Children as Informants of Bullying Victimization: Results from an Epidemiological Cohort of Children. Journal of Abnormal Child Psychology, 39(3), 379–387. https://doi.org/10.1007/s10802-010-9463-5

Silberg, J. L., Copeland, W., Linker, J., Moore, A. A., Roberson-Nay, R., & York, T. P. (2016). Psychiatric outcomes of bullying victimization: A study of discordant monozygotic twins. Psychological Medicine, 46(9), 1875–1883. https://doi.org/10.1017/S0033291716000362

Singham, T., Viding, E., Schoeler, T., Arseneault, L., Ronald, A., Cecil, C. M., McCrory, E., Rijsdijk, F., & Pingault, J.-B. (2017). Concurrent and Longitudinal Contribution of Exposure to Bullying in Childhood to Mental Health: The Role of Vulnerability and Resilience. JAMA Psychiatry, 74(11), 1112–1119. https://doi.org/10.1001/jamapsychiatry.2017.2678

Soneson, E., Puntis, S., Chapman, N., Mansfield, K. L., Jones, P. B., & Fazel, M. (2022). Happier during lockdown: A descriptive analysis of self-reported wellbeing in 17,000 UK school students during Covid-19 lockdown. European Child & Adolescent Psychiatry. https://doi.org/10.1007/s00787-021-01934-z

Sullivan, T. N., Farrell, A. D., Sutherland, K. S., Behrhorst, K. L., Garthe, R. C., & Greene, A. (2021). Evaluation of the Olweus Bullying Prevention Program in US Urban Middle Schools Using a Multiple Baseline Experimental Design. Prevention Science: The Official Journal of the Society for Prevention Research, 22(8), 1134–1146. https://doi.org/10.1007/s11121-021-01244-5

Thornberg, R. (2018). School bullying and fitting into the peer landscape: A grounded theory field study. British Journal of Sociology of Education, 39(1), 144–158. https://doi.org/10.1080/01425692.2017.1330680

Ttofi, M. M., Bowes, L., Farrington, D., & Lösel, F. (2014). Protective Factors Interrupting the Continuity From School Bullying to Later Internalizing and Externalizing Problems: A Systematic Review of Prospective Longitudinal Studies. https://doi.org/10.1080/15388220.2013.857345

Ttofi, M. M., Farrington, D. P., & Lösel, F. (2012). School bullying as a predictor of violence later in life: A systematic review and meta-analysis of prospective longitudinal studies. Aggression and Violent Behavior, 17(5), 405–418. https://doi.org/10.1016/j.avb.2012.05.002

UNESCO, The United Nations Educational, Scientific and Cultural Organization. (2016). Global guidance on addressing school-related gender-based violence. https://unesdoc.unesco.org/ark:/48223/pf0000246651

UNESCO, The United Nations Educational, Scientific and Cultural Organization. (2019). Behind the numbers: Ending school violence and bullying, 2019. https://unesdoc.unesco.org/ark:/48223/pf0000366483

UNESCO, The United Nations Educational, Scientific and Cultural Organization. (2021). Violence and bullying in educational settings: The experience of children and young people with disabilities. https://unesdoc.unesco.org/ark:/48223/pf0000378061

Ungar, M., & Theron, L. (2020). Resilience and mental health: How multisystemic processes contribute to positive outcomes. The Lancet Psychiatry, 7(5), 441–448. https://doi.org/10.1016/S2215-0366(19)30434-1

Vaillancourt, T., Brittain, H., Krygsman, A., Farrell, A. H., Landon, S., & Pepler, D. (2021). School bullying before and during COVID-19: Results from a population-based randomized design. Aggressive Behavior, 47(5), 557–569. https://doi.org/10.1002/ab.21986

Vaillancourt, T., Duku, E., Decatanzaro, D., Macmillan, H., Muir, C., & Schmidt, L. A. (2008). Variation in hypothalamic–pituitary–adrenal axis activity among bullied and non-bullied children. Aggressive Behavior, 34(3), 294–305. https://doi.org/10.1002/ab.20240

Vaillancourt, T., McDougall, P., Hymel, S., Krygsman, A., Miller, J., Stiver, K., & Davis, C. (2008). Bullying: Are researchers and children/youth talking about the same thing?: International Journal of Behavioral Development. https://doi.org/10.1177/0165025408095553

Valmaggia, L. R., Latif, L., Kempton, M. J., & Rus-Calafell, M. (2016). Virtual reality in the psychological treatment for mental health problems: A systematic review of recent evidence. Psychiatry Research, 236, 189–195. https://doi.org/10.1016/j.psychres.2016.01.015

Vivolo-Kantor, A. M., Martell, B. N., Holland, K. M., & Westby, R. (2014). A systematic review and content analysis of bullying and cyber-bullying measurement strategies. Aggression and Violent Behavior, 19(4), 423–434. https://doi.org/10.1016/j.avb.2014.06.008

Vrijen, C., Wiertsema, M., Ackermans, M. A., Ploeg, R. van der, & Kretschmer, T. (2021). Childhood and Adolescent Bullying Perpetration and Later Substance Use: A Meta-analysis. Pediatrics, 147(3). https://doi.org/10.1542/peds.2020-034751

Warren, E., Melendez-Torres, G. J., Viner, R., & Bonell, C. (2020). Using qualitative research to explore intervention mechanisms: Findings from the trial of the Learning Together whole-school health intervention. Trials, 21(1), 774. https://doi.org/10.1186/s13063-020-04688-2

Wienke Totura, C. M., Green, A. E., Karver, M. S., & Gesten, E. L. (2009). Multiple informants in the assessment of psychological, behavioral, and academic correlates of bullying and victimization in middle school. Journal of Adolescence, 32(2), 193–211. https://doi.org/10.1016/j.adolescence.2008.04.005

Wolke, D., Lee, K., & Guy, A. (2017). Cyberbullying: A storm in a teacup? European Child & Adolescent Psychiatry, 26(8), 899–908. https://doi.org/10.1007/s00787-017-0954-6

Wolke, D., & Skew, A. J. (2012). Bullying among siblings. International Journal of Adolescent Medicine and Health, 24(1), 17–25. https://doi.org/10.1515/ijamh.2012.004

Yun, H.-Y., & Salmivalli, C. (2021). The KiVa Anti-Bullying Program. In The Wiley Blackwell Handbook of Bullying (pp. 430–449). John Wiley & Sons, Ltd. https://doi.org/10.1002/9781118482650.ch57

Zych, I., Farrington, D. P., & Ttofi, M. M. (2019). Protective factors against bullying and cyberbullying: A systematic review of meta-analyses. Aggression and Violent Behavior, 45, 4–19. https://doi.org/10.1016/j.avb.2018.06.008

Zych, I., Ttofi, M. M., & Farrington, D. P. (2019). Empathy and Callous-Unemotional Traits in Different Bullying Roles: A Systematic Review and Meta-Analysis. Trauma, Violence & Abuse, 20(1), 3–21. https://doi.org/10.1177/1524838016683456

Zych, I., Ttofi, M. M., Llorent, V. J., Farrington, D. P., Ribeaud, D., & Eisner, M. P. (2020). A Longitudinal Study on Stability and Transitions Among Bullying Roles. Child Development, 91(2), 527–545. https://doi.org/10.1111/cdev.13195

Zych, I., Viejo, C., Vila, E., & Farrington, D. P. (2021). School Bullying and Dating Violence in Adolescents: A Systematic Review and Meta-Analysis. Trauma, Violence & Abuse, 22(2), 397–412. https://doi.org/10.1177/1524838019854460