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Study within the SCARS project to examine neural and behavioral responses to social exclusion, measured through the fMRI Cyberball task and questionnaires afterwards, and how these responses relate to victimization experiences.

Little is known about how friendship quantity, quality, and stability predict and are predicted by social withdrawal in adolescence, and no study has examined the relations between changes in these friendship characteristics and withdrawal. The current study tested a moderated mediation model. In this model, the continuity of social withdrawal is mediated by baseline levels and changes in the adolescent’s friendship network, transition status moderates the associations between withdrawal and friendship characteristics, and sex moderates all paths. Because number of friends, friendship quality, and friendship stability are interrelated, all three characteristics were modeled simultaneously in order to identify their unique mediating effects. We aimed to answer three questions: (1) do baseline levels and changes in friendship quantity, quality, and stability mediate the continuity (or discontinuity) of withdrawal from 16 to 19 years? (2) do education and house transitions moderate the association from pre-transition withdrawal to changes in friendship network characteristics? (3) Does sex moderate any of the paths in the mediation model?

Many studies report that specific exposures predict risk for later maladjustment and the exposure is often, either explicitly or implicitly, presented as part of a causal mechanism. Genetic vulnerabilities are usually not taken into account, although these may confound the reported associations. Recently presented evidence suggests that large proportions of the associations between the phenotypes maternal education and child educational achievement, body mass index, and attention-deficit hyperactivity disorder are in fact explained by genetic confounding (Pingault et al., 2020). Causal claims are also prominently present in bullying research. In a recently published meta-analysis on outcomes of bullying victimization (Moore et al., 2017), the authors explicitly stated that there was strong evidence of a causal link between being a victim of bullying and developing internalizing symptoms, i.e., that being bullied causes depression, anxiety, and suicidal ideation. Genetic vulnerability was not taken into account. If genetic vulnerability explains both being a victim of bullying and internalizing symptoms, the reported prospective association between bullying victimization and internalizing symptoms is spurious rather than causal. Bullying perpetration has been linked to later externalizing problems, i.e., offending (Ttofi et al., 2012) and substance use (Ttofi et al., 2016; Vrijen et al., 2021). Although the authors of these meta-analyses (one of which is from our own research group) did not make explicit claims about causality based on their own findings, they did suggest that investigating whether changes in bullying precede changes in offending and substance use could shed light on the plausibility of a causal mechanism. Although temporality is a necessary condition for causality, it is not a sufficient condition and a shared genetic vulnerability may still explain both bullying perpetration and later externalizing problems. In the present study, the associations between bullying involvement and later maladjustment that are most strongly supported by meta-analytic evidence will be revisited by investigating to what extent genetic confounding can account for the reported associations. For the main analyses, the overarching constructs of internalizing and externalizing problems are used as outcomes. The studied prospective associations are: (1) bullying victimization -> internalizing problems; (2) bullying perpetration -> externalizing problems. We will use polygenic scores to estimate the proportions of the reported phenotypic associations explained by genetic vulnerability. Because polygenic scores capture only a small part of heritability, controlling for polygenic scores cannot entirely capture genetic confounding. Twin-study-based heritability estimates for bullying victimization and perpetration are, respectively ~ 70% and ~ 65% (Veldkamp et al., 2019), between 61% and 80% for externalizing problems (Hicks et al., 2004; Kendler et al., 2016) and ~ 50% for internalizing problems (Franić et al., 2014; Nivard et al., 2015). SNP heritability is much lower (Pingault et al., 2020) and heritability estimates based on polygenic scores are only a small fraction of twin-study-based heritability estimates. We will therefore use a recently proposed novel method (Pingault et al., 2020) that extends the use of observed polygenic scores with a sensitivity analysis in which structural equation models are used to examine how an increase in the predictive power of polygenic scores based on SNP heritability and twin-study-based total heritability estimates would affect the reported associations between bullying involvement and later maladjustment.

The aim of this study was to test a longitudinal, transactional model that describes how social withdrawal and friendship development are interrelated in late adolescence, and to investigate if post-secondary transitions are catalysts of change for withdrawn adolescents’ friendships. Unilateral friendship data of 1,019 adolescents (61.3% female, 91% Dutch-origin) from the Tracking Adolescents' Individual Lives Survey (TRAILS) were collected five times from ages 17 to 18 years. Social withdrawal was assessed at 16 and 19 years. The transactional model was tested within a Structural Equation Modelling framework, with intercepts and slopes of friendship quantity, quality, and stability as mediators and residential transitions, education transitions, and sex as moderators. The results confirmed the presence of a transactional relation between withdrawal and friendship quality. Whereas higher age 16 withdrawal predicted having fewer, lower-quality, and less-stable friendships, only having lower-quality friendships, in turn, predicted higher age 19 withdrawal, especially in girls. Residential transitions were catalysts of change for withdrawn youth’s number of friends: higher withdrawal predicted a moderate increase in number of friends for adolescents who relocated, and no change for those who made an educational transition or did not transition. Taken together, these results indicate that the quality of friendships—over and above number of friends and the stability of those friendships—is particularly important for entrenching or diminishing withdrawal in late adolescence, and that relocating provides an opportunity for withdrawn late adolescents to expand their friendship networks.

Study within the SCARS project to examine how emotions of others are processed, both with a behavioral task as well as an fMRI task, and how it relates to the negative experience of being bullied.

Contains fulltext : 282224.pdf (Publisher’s version ) (Open Access) The aim of this study was to test a longitudinal, transactional model that describes how social withdrawal and friendship development are interrelated in late adolescence, and to investigate if post-secondary transitions are catalysts of change for highly withdrawn adolescents’ friendships. Unilateral friendship data of 1,019 adolescents (61.3% female, 91% Dutch-origin) from the Tracking Adolescents’ Individual Lives Survey (TRAILS) cohort were collected five times from ages 17 to 18 years. Social withdrawal was assessed at 16 and 19 years. The transactional model was tested within a Structural Equation Modeling framework, with intercepts and slopes of friendship quantity, quality, and stability as mediators and residential transitions, education transitions, and sex as moderators. The results confirmed the presence of a transactional relation between withdrawal and friendship quality. Whereas higher age 16 withdrawal predicted having fewer, lower-quality, and less-stable friendships, only having lower-quality friendships, in turn, predicted higher age 19 withdrawal, especially in girls. Residential transitions were catalysts of change for highly withdrawn youth's number of friends: higher withdrawal predicted a moderate increase in number of friends for adolescents who relocated, and no change for those who made an educational transition or did not transition. Taken together, these results indicate that the quality of friendships - over and above number of friends and the stability of those friendships - is particularly important for entrenching or diminishing withdrawal in late adolescence, and that relocating provides an opportunity for withdrawn late adolescents to expand their friendship networks. 21 p.

Pre-analysis preregistration for project: A New School, a Fresh Start? (Dis)continuation of Positive and Negative Peer Experiences across the Transition from Primary to Secondary School, and its Impact on Academic Achievement. Based on the template https://osf.io/t6m9v/, adapted for pre-analysis purposes. A. Hypotheses Introduction and Description of essential elements The transition from primary to secondary school brings along many changes for students. Secondary schools are often larger and further away from home, students are tracked into educational levels, educated by new teachers for every subject, and expected to work more independently. This transition coincides with the onset of adolescence in which great biological, social, and cognitive changes that enhance the importance of peers (Veenstra & Laninga‐Wijnen, 2023). Out of all changes, students worry most about their peer relationships because they enter a large, unfamiliar peer group (Jindal-Snape et al., 2021). Already in the first weeks after the transition to secondary school, students establish their social position in the peer group (de Vries et al., 2021; Laninga‐Wijnen et al., 2019). This transition can be a turning point in students’ social relationships (Elder, 1985), and therefore is often considered as a possible ‘fresh start’ in terms of peer experiences. Nevertheless, the transition may pose a risk to the social lives of many students (for a review, see: Jindal-Snape et al., 2021). Students also face academic challenges when transitioning to secondary school. Many students’ grades decline following the transition to secondary school (e.g., Felmlee et al., 2018), and their school engagement decreases over adolescence (Engels et al., 2017). These social and academic difficulties have long-term negative consequences, including lowered educational attainment (Lorijn et al., 2022). Previous studies confirm that school transitions are an important turning point in students’ social lives (Jindal-Snape et al., 2021) but the role of peer relationships in the transition from primary to secondary school needs further attention for two reasons. First, most previous studies took a variable-centered approach in examining mean level changes in social outcomes, overlooking individual differences. Therefore, it remains unclear how students’ previous peer experiences (dis)continue over the transition. Key aspects of students’ peer experiences in school include peer attachment, loneliness, and victimization. Examining the within-person constellation of these facets, we can study how students with more positive experiences (i.e., scoring higher on attachment and lower on victimization and loneliness) and more negative peer experiences (i.e., vice versa), maintain or change these experiences when entering a new peer context in secondary school. For instance, do students with negative peer experiences in primary school make a fresh start and have positive peer experiences in secondary education, or do the negative peer experiences continue? Insight into within-person changes in peer experiences over school transitions provides knowledge on which students may socially be most at risk. Second, some previous research examined both social and academic outcomes in school transitions and found these were related (e.g., Felmlee et al., 2018). This raises the question to what extent changes in peer experiences predict student’s academic achievement, as being socially integrated in the peer context is essential for students’ academic achievement (Ryan & Shin, 2018). For instance, if negative peer experiences diminish after the transition to secondary school, does this relate to higher academic achievement or do early negative peer experiences have long-term negative effects for academic achievement? Examining the relation between social and academic outcomes broadens our understanding of how a fresh start in terms of peer experiences matters for academic achievement. Taken together, this study builds upon existing literature by examining (1) to what extent students’ within-person constellation of peer experiences (i.e., attachment, victimization, and loneliness) (dis)continues over the transition from primary to secondary school, and (2) how this (dis)continuation relates to academic achievement in secondary school. Theory and Hypotheses Peer Experiences & Academic Achievement Following Self-Determination Theory, relatedness is essential for students’ academic motivation and development (Ryan & Deci, 2000). Relatedness describes the need to belong to a social group and prevent social exclusion (Baumeister & Leary, 1995). For adolescents, belonging to peers is of particular importance because major biological, social, and cognitive changes enhance the importance of peers in this stage of life (Veenstra & Laninga‐Wijnen, 2023). At school, relatedness can thus be fostered by belonging to the peer group and enjoying positive peer experiences while avoiding negative peer experiences. Positive peer experiences promote students’ academic motivation and development in several ways, such as by fostering school well-being (Kiuru et al., 2020), self-efficacy, and engagement (Wentzel et al., 2021). Attachment to classmates, feelings of loneliness and victimization are important facets of students’ peer experiences in school that impact students’ academic achievement. Students’ attachment to peers is generally defined as sharing a deep and enduring emotional bond (Bowlby, 1973). In the school context, peer attachment for instance reflects feeling of acceptance and being understood by classmates. Being more accepted by classmates is related to higher academic achievement (Wentzel et al., 2021). Loneliness is the unpleasant feeling which occurs when there is a discrepancy between a person’s perceived and desired quantity or quality of social relationships (Perlman & Peplau, 1981). Considering the importance of peers for adolescents, peer-related loneliness is detrimental for students. At school, feeling lonely among peers for instance entails feeling excluded by classmates. Victimization refers to a student repeatedly being exposed to goal-directed aggressive actions by one or more classmates in the context of a power imbalance (Olweus, 1993). These aggressive actions can take different forms, including physical, relational, material and cyber-victimization. Students who are victimized or lonely encounter heightened educational difficulties (Heinrich & Gullone, 2006; Kretschmer et al., 2018). Taken together, the within-person constellation of experiencing more peer attachment, lower loneliness, and lower victimization reflects positive peer experiences that foster academic achievement. The within-person constellation of being less attached, more lonely, and more victimized reflects negative peer experiences that hinder academic achievement. (Dis)continuation of Peer Experiences across School Transitions The transition to a new peer group in secondary education facilitates the opportunity to change students’ peer experiences. Nevertheless, peer experiences continue over the transition from primary to secondary school for many students. Students’ peer status is relatively stable over time (Engels et al., 2019). This is in line with attachment theory’s arguing that early attachment relationships set the stage for later attachment relationships (Bowlby, 1973). Focusing on the transition, students’ loneliness before the transition to middle school was strongly correlated with their loneliness after the transition (Kingery et al., 2011). Students who were more accepted by peers and had more and higher quality friendships prior to the transition, were less lonely after the transition (Kingery et al., 2011). Moreover, making new friends in secondary school was especially difficult for students with negative peer experiences such as victimization in primary school (Evangelou et al., 2008), suggesting that negative peer experiences continue for some students. In addition, self-esteem remained stable over the transition from primary to secondary school, and was related to being accepted by classmates (Poorthuis et al., 2014). Possibly, students with positive peer experiences in primary education have the social network and social skills to re-establish this position in secondary education, and vice versa. Students’ peer experiences may particularly remain stable when they make the same transition as their primary school classmates (Temkin et al., 2018). For instance, students kept the same friends if they made the same transition as their classmates from primary school, whereas friendships were more often disrupted when students transitioned to a new peer group (Temkin et al., 2018). We tentatively expected that, for most students, peer experiences would remain stable across the transition from primary to secondary school. Drawing upon life-course theories, difficult life transitions such as school transitions can greatly impact social relationships (Almeida & Wong, 2009; Elder, 1985). For some students, peer experiences may thus discontinue over the transition from primary to secondary school. For these students, school transitions generally pose a risk to their social lives. In a recent review on school transitions, ten studies reported a negative impact of the transition on their peer experiences, while seven studies reported an improvement in peer experiences (Jindal‐Snape et al., 2020). Students who change schools have fewer friends and were more likely to become isolates after a school transition compared with students who do not change schools (Felmlee et al., 2018; Temkin et al., 2018). Of the students who change schools, roughly 50% has fewer friends after the transition, 30% gains friends, and 20% has a stable number of friendships across the transition (Felmlee et al., 2018). Besides students’ number of friendships, students who change schools have more disrupted friendships, less dense friendship networks, are more socially distant from other students, and have more segregated friendship networks (Temkin et al., 2018). These drawbacks for students’ friendships are long lasting, and persist throughout high school (Felmlee et al., 2018). Moreover, students may feel more lonely after the transition to secondary school due to the shift to an unfamiliar context (Benner, 2011; Benner & Graham, 2009). In addition, as bullying peaks and bullies become more strategic over adolescence, students are at risk for intensified victimization (Pellegrini & Long, 2002). Therefore, positive peer experiences may decrease especially for students with more positive peer experiences in primary school. Taken together, we tentatively expected that some students with positive peer experiences in primary school would transition toward having more negative peer experiences in secondary school. Despite this average negative impact, for some students, the transition to secondary school may facilitate a ‘fresh start’ to improve the peer experiences of others. For these students, the transition is an opportunity to establish new peer relationships from a wider group of peers, and enhance their social status in the new group (Jindal‐Snape et al., 2020). Particularly students with negative peer experiences in primary school may benefit from school transitions. For instance, particularly students with fewer friends compared to their peers in primary education, gained friends after the transition to secondary education (Felmlee et al., 2018). More diverse subgroups of students in secondary school give students who previously felt left out an opportunity to fit into the peer group (Kinney, 1993). Moreover, meeting a new, large pool of possible friends may decrease students’ feelings of loneliness (Barber & Olsen, 2004; Lorijn et al., 2022). In addition, victimization decreases more and aggressive behavior is less socially rewarded in schools with a transition compared to schools without a transition (Farmer et al., 2011; Wang et al., 2016). Possibly, school transitions lead to a reorganization of the social hierarchy in the classroom, offering the possibility for students to improve their social status in the new peer group. Taken together, it may be that some students with negative peer experiences in primary school enjoy a ‘fresh start’ when entering secondary school. We explored to what extent students with negative peer experiences in primary school would transition toward having more positive peer experiences in secondary school. Academic Consequences of Changing Peer Experiences Peer experiences impact students’ academic achievement (Ryan & Deci, 2000; Ryan & Shin, 2018), also across school transitions. For instance, students’ peer acceptance and number and quality of friendships prior to the transition to middle school predicted academic achievement after this school transition (Kingery et al., 2011). These primary school peer experiences accounted for 15% of the variance in academic achievement in secondary school while accounting for students’ achievement in primary school (Kingery et al., 2011). Possibly, students with positive peer experiences can rely on their social and emotional resources while navigating academic challenges during the transition. The relation between peer experiences and academic achievement raises the question to what extent changes in peer experiences over school transitions relate to students’ academic achievement. Based on the reasoning that positive peer experiences foster academic achievement whereas negative peer experiences lower academic achievement, we expected that students with continued positive peer experiences from primary to secondary school would have the highest academic achievement compared with students with negative peer experiences at some point (Hypothesis 1). Conversely, students with continued negative peer experiences may be the worst off academically in secondary school. For these students, the transition may particularly have a negative effect on their academic achievement. Students with negative peer experiences in primary school may view the transition to a new peer context as an opportunity to improve their social stance in the peer group. Failure of improving their social position may cause an additional setback to their self-esteem and well-being as these students may attribute the negative peer experiences to themselves (‘it must be me’) rather than to others (‘it could be them’) (Huitsing et al., 2012). Taken together, we expected that students with continued negative peer experiences from primary to secondary school would have the lowest academic achievement compared with students with positive peer experiences at some point (Hypothesis 2). Failing to re-establish positive peer experiences in secondary school may undermine student’s academic achievement. Possibly, students who had positive peer experiences in primary education anticipate that they will re-establish their positive social position in the classroom (Poorthuis et al., 2014). Yet, a discrepancy between students’ anticipation in primary school and their actual peer experiences in secondary school may have a negative effect on their self-esteem (Poorthuis et al., 2014). The negative impact of failure to re-establish students’ social position may be reinforced by the increased importance of peers (Veenstra & Laninga‐Wijnen, 2023), the decline in school engagement in adolescence (Engels et al., 2017), and the negative impact of the transition on academic achievement (Felmlee et al., 2018). Therefore, we expected students changing their positive experiences to negative experiences would achieve lower compared with students with only positive experiences, and higher than students with only negative experiences (Hypothesis 3). Students who change from having negative peer experiences in primary school to having positive peer experiences in secondary school may enjoy a fresh start not only socially, but also academically. Positive peer experiences may boost their self-esteem and school well-being, making them academically flourish (Wentzel et al., 2021). We expected that students changing their negative experiences to positive experiences (i.e., having a ‘fresh start’) would achieve higher compared with students with only negative experiences, and lower than students with only positive experiences (Hypothesis 4). It remains unclear to what extent students changing from positive to negative peer experiences differ from students changing from negative to positive peer experiences. On the one hand, peer experiences become increasingly important in adolescence (Veenstra & Laninga‐Wijnen, 2023), which make negative peer experiences in secondary education particularly detrimental. On the other hand, early peer experiences may be most important and lay a base for students’ long-term self-worth and cognitive development (Bowlby, 1973). Therefore, we will explore differences in academic achievement between students who change from positive to negative experiences, with that from students who change from negative to positive experiences (i.e., having a ‘fresh start’). Summarized Hypotheses This study investigated (1) how students’ peer experiences (dis)continue over the transition from primary to secondary school, and (2) how this (dis)continuation relates to students’ academic achievement in secondary school. We explore peer experience groups based on students’ combined scores on peer attachment, loneliness, and victimization in primary and secondary school. Positive peer experiences are characterized by more peer attachment, lower loneliness and lower victimization, and vice versa for negative peer experiences. Due to our person-centered approach, we explore how students transition between peer experience groups and we therefore solely suggest tentative hypotheses regarding these transitions. We tentatively expected that, for most students, peer experiences would remain stable across the transition from primary to secondary school, because peer experiences are relatively stable over time (Engels et al., 2019). Following life-course theories, some students may have changing peer experiences over this transition (Almeida & Wong, 2009; Elder, 1985). As students’ social outcomes on average decline across the transition from primary to secondary school lives (Jindal-Snape et al., 2021), we tentatively expected that some students with positive peer experiences in primary school would transition toward having more negative peer experiences in secondary school. We explored to what extent students with negative peer experiences in primary school would transition toward having more positive peer experiences in secondary school (i.e., having a ‘fresh start’). Based upon the Self-Determination Theory (Ryan & Deci, 2000), we argue that the (dis)continuation of peer experiences relates to students’ academic achievement in secondary school. We expected that students with continued positive peer experiences from primary to secondary school would have the highest academic achievement compared with students with negative peer experiences at some point (Hypothesis 1). We expected that students with continued negative peer experiences from primary to secondary school would have the lowest academic achievement compared with students with positive peer experiences at some point (Hypothesis 2). We expected students changing their positive experiences to negative experiences would achieve lower compared with students with only positive experiences, and higher than students with only negative experiences (Hypothesis 3). We expected that students changing their negative experiences to positive experiences (i.e., having a ‘fresh start’) would achieve higher compared with students with only negative experiences, and lower than students with only positive experiences (Hypothesis 4). We explore differences in academic achievement between students who change from positive to negative experiences, compared with students who change from negative to positive experiences (i.e., having a ‘fresh start’). B. Methods Description of variables Independent variables Loneliness (T1, T2). In PRIMS, we measured loneliness using 5 items of the peer-related loneliness subscale of the Loneliness and Aloneness scale for Children and Adolescents (Also see Lorijn et al., 2022; LACA; Marcoen et al., 1987). Sample items are ‘I feel left out by my friends’, ‘I feel sad because I have no friends’, and ‘I feel alone at school’. Students rated the items as 1 = never to 4 = always. The scale was generated by averaging the answers on the items for every student with a valid response to at least two items. The scale revealed good reliability scores for T2 (α = .847) and T3 (α = .883). Victimization (T1, T2). Victimization was measured by asking ‘Can you indicate how often you have been bullied at school in the past months?’ (Also see Lorijn et al., 2022). Before asking this question, students saw an introduction clip providing the definition of bullying in the first two waves of the second PRIMS cohort (Kaufman et al., 2018; Olweus, 1996). Students rated the question as 1 = never to 5 = several times a week. Peer Attachment (T1, T2). We inventoried students’ peer attachment using the trust subscale of the Inventory of Parent and Peer Attachment (IPPA; Armsden & Greenberg, 1987). We adapted the original items that focused on friends and parents to fit classmates. The scale comprises three items: ‘My classmates accept me as I am’, ‘My classmates respect my feelings’, and ‘When I am angry about something, my classmates try to be understanding’. Students rated the items as 1 = never to 4 = always. The scale was generated by averaging the answers on the items for every participant with a valid response to at least two items. The scale revealed good reliability scores for T2 (α = .775) and T3 (α = .794). Dependent variables Academic achievement (T2). Academic achievement was measured by students’ self-reported grade for Mathematics, Dutch and English on their last report card. Grades ranged from 1 till 10 being rounded on two decimals, with higher numbers indicating higher grades. Grades for Mathematics, Dutch and English all significantly positively correlated at the 0.01 level (r = .134 or higher). Grades were averaged to compile one average grade as a proxy for academic achievement for every student with a valid score for at least one subject. Covariates Control variables. To assess gender, students indicated if they were a boy, girl, or other. Because only four students (0.5%) indicated to be ‘other’, we coded ‘other’ missing and gender as 0 = boy; 1 = girl. If possible, we will link our data to register data to control for students’ academic achievement in their last year of primary school measured by students’ score on their standardized exit-test (most often the ‘Cito-test’), and the number of primary school classmates that join the same secondary school calculated by the location of students’ secondary schools. Sample Data stem from the PRIMS project (an acronym for the transition from PRIMary to Secondary education). PRIMS aimed to study the role of peers in the transition from primary to secondary education in The Netherlands, and followed participants over this transition. PRIMS comprises two cohorts including multiple waves, with this study using data of the second wave (primary school) and third wave (secondary school) of the second cohort. The data in primary school were collected in May and June 2021, during students’ last months in primary education. Data in secondary school were conducted in January and February 2022, roughly five months after the students transitioned to secondary education. The educational system in the Netherlands consists of primary and secondary education. Students attend primary education from when they are four years old until they are eleven or twelve years old, when they transition to secondary education. Students attend secondary education until they are between sixteen and eighteen years old, depending on their track. In secondary education, students are tracked in different ability groups from pre-vocational secondary education to pre-university education. For the second cohort of the PRIMS project, we selected schools that participated in the first PRIMS cohort, supplemented with a new school sample. We invited all 66 schools that participated in the first cohort to partake in the second cohort, with 33 of these schools (50%) initially being willing to participate. We drew an additional sample of 318 schools to supplement the schools that continued to participate in the second cohort, aiming for a final sample of 100 schools. For both cohorts, we used a stratified sampling design to select schools, with the sample frame consisting of the full population of Dutch primary schools. For the sampling of the second cohort, we took into account the characteristics of the 33 schools willing to participate in both cohorts, and we adjusted our expected response rates based on the response rate of the first cohort. Out of the 318 supplementary sampled schools for the second cohort, 53 agreed to participate (16.7%). The 33 schools from the first cohort initially willing to participate in the second cohort dropped to 25, mainly due to time constraints related to the COVID-19 pandemic. In total, 79 schools with 120 classes agreed to participate in the second cohort, resulting in a representative sample on region, level of urbanization, socio-economic composition and test scores at the school level. In the second wave (our measure for primary school), 79 schools participated, including 77 schools that also participated in the first wave and two schools that entered the study in the second wave. We invited all 2,673 students who were in their final year of primary education (Dutch grade 8, 11-12 years old) of the participating schools to take part. Of the invited students, 1,676 (62.7%) obtained active parental consent to participate. In total, 1,634 students participated for our primary school measure. The remaining students did not participate mainly because they were absent at the time. Students filled out the online survey during regular school hours under supervision of their teacher, which took approximately 45 minutes. We invited all students who participated in the first or second wave to participate in the secondary school wave. In total, 784 students participated in secondary school. The remaining students were not in their last year of primary education at primary school at wave one, did not provide valid contact details or did not reply. Students filled out the online survey of approximately 15 minutes at home. As an incentive to complete the secondary school wave, students could join a lottery to win a Nintendo Switch. Of the 784 students who participated in secondary school, 758 students also participated in T1. In sum, 758 students (Mage wave 1 = 11.57, SD = 0.56; 53.5% girls, 0.9 % missing values on gender) from 105 primary school classes and 77 primary schools are included in our analyses sample. C. Analysis plan Confirmatory analyses We performed three steps of statistical analyses to test our hypothesis in Mplus version 8.5 (Muthén & Muthén, 2017). First, we conducted latent class analyses (LCA) to explore peer experience groups within our data. LCA is a person-centered approach that groups individuals into classes based on their scores on the included variables. We identified peer experience groups based on the students’ combined scores on peer attachment, loneliness and victimization. We performed cross-sectional LCA on both time points and longitudinal LCA, to check if the same peer experience groups were distinguished on both time points. The optimal number of classes was determined based on five criteria. Our first criterion is the Bayesian Information Criterion (BIC), which shows whether adding a class improves the model fit, with the lowest aBIC value indicating the best fit. The second criterion is the Entropy value (E), which should be ≥ .80 to indicate a good fit. The third criterion is the Lo-Mendell-Rubin Likelihood Ratio Test (LMR-LRT), which should be significant to indicate an improvement in model fit when adding a class. Our fourth criterion states that the size of the additional class should not be lower than 5.0% of the sample. As a fifth criterion, adding a class should provide unique theoretical information. Second, we performed latent transition analyses (LTA) to explore how students transition between peer experiences groups in the transition from primary to secondary education. We first explored the number of students per class on both time points, to investigate if classes change in size. We secondly explored students’ transitions between classes based on transition probabilities, explaining changes in class sizes. Based on students’ transitions between classes, we identified, number and name the trajectories. Third, we used linear regression analyses to test our confirmatory hypotheses on how students’ peer experience trajectories relate to students’ academic achievement in secondary education. Model fit was assessed using R2 and residuals between the values and predicted values. Alternative plan Option 1: We explore how students transition between peer experience groups across the transition from primary to secondary school using LTA. We may not find all four possible trajectories (i.e., stable positive experiences, stable negative experiences, changing positive to negative experiences, changing negative to positive experiences). Therefore, we may not be able to test all confirmatory hypothesis on how these trajectories relate to students’ academic achievement in secondary school. We particularly foresee the possibility that only stable trajectories are found because the number of students with negative peer experiences is limited. If we find fewer trajectories, we will only test the hypothesis of the trajectories found. Option 2: It may be that LTA cannot be computed because no measurement invariance is found for the longitudinal LCA’s, or the peer experience groups resulting from the LCA’s are too small to detect differences in transitions. In this case, a variable centered approach may be preferred over a person-centered approach. If needed, we can replace the LTA by linear and ordinal logistic regressions of peer attachment, loneliness, and victimization in primary school as predictors of peer attachment, loneliness, and victimization in secondary school. Change scores can be used in a linear regression of changes in peer experiences on academic achievement in secondary school. Method of missing data handling Missing data due to attrition reduced our sample from 1,634 (of which 1409 grade 6 students at wave 2) to 758 students. We perform sensitivity analyses to examine to what extent students in our analyses sample (n = 758) differ from grade 6 students who were not our in sample (n = 651) in gender, peer attachment, loneliness, victimization, and academic achievement. In the main analyses, partially missing values on key variables were handled using the full information maximum likelihood estimate (Muthén & Muthén, 2017). We consider possible selectivity of our sample in giving conclusions of our results. Assumptions of analyses To apply LTA, there must be at least two repeated measures, and there must be measurement invariance for the longitudinal LCA’s (Morin & Litalien, 2017). There are two repeated measure of all variables needed to create the peer experience groups. To test if there is measurement invariance, we examine if the peer experiences groups found on both timepoints have similar within-class means: we test the model fit by the Entropy value for a model in which the within-class means are held equal for both time points. If this assumption cannot be met, we continue with option 2 of the alternative methods described above above. Answer the following final questions: Has data collection begun for this project? o No, data collection has not begun x Yes, data collection is underway or complete If data collection has begun, have you looked at the data? x Yes o No The (estimated) start and end dates for this project are (optional): The data were collected between January 2021 and February 2022. Any additional comments before I pre-register this project (optional): As stated above the data was already collected. The main researchers in this study contributed to collecting data in the longitudinal PRIMS-study. This included adapting surveys for upcoming waves and data cleaning. Therefore, researchers were aware of the means and reliability scores of the variables in the study. However, no preparatory analysis giving information on relations between variables in this study were conducted. Furthermore, we are open about our exploratory analyses and all confirmatory hypotheses are based on theory and not on the mean scores of the variables. Therefore, this pre-registration may be considered valid as a pre-analysis pre-registration for longitudinal data. References Almeida, D. M., & Wong, J. D. (2009). Life transitions and daily stress processes. In G. H. Elder & J. Z. Giele (Eds.), The craft of life course research (pp. 141–162). The Guilford Press. Armsden, G. C., & Greenberg, M. T. (1987). The inventory of parent and peer attachment: Individual differences and their relationship to psychological well-being in adolescence. Journal of Youth and Adolescence, 16(5), 427–454. Barber, B. 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