This study examined (a) the predictive link between peer victimization and children's reactive and proactive aggression, and (b) the potential moderating effect of reciprocal friends' reactive and proactive aggression in this context. The study also examined whether these potential moderating effects of friends' characteristics were stronger with respect to more recent friends compared to previous friends. Based on a convenience sample of 658 twin children (326 boys and 332 girls) assessed in kindergarten and first grade, the results showed that peer victimization uniquely predicted an increase in children's teacher-rated reactive aggression, but not teacher-rated proactive aggression. The relation of peer victimization to increased reactive aggression was, however, moderated by recent not previous reciprocal friends' similarly aggressive characteristics. These findings, however, tended to be mostly true for boys, but not for girls. The findings are discussed in terms of their theoretical and practical implications for victimized children's risk of displaying reactive and proactive aggressive behaviors.

Based on the notion that friendship may serve an important protective function against peer victimization, this study examined the moderating effect of reciprocal friends' prosociality on the link between a child's reactive aggression and victimization. The study also investigated whether a similar moderating effect could be found with respect to sibling's prosociality, given that sibling relationships have been found to provide social benefits comparable to friendships. These questions were addressed using a sample of 246 six-year-old twin pairs (246 boys and 246 girls). The results showed that a child's own reactive aggression uniquely contributed to the risk of victimization for both boys and girls. The link between reactive aggression and victimization was, however, moderated by reciprocal friends' prosocial behavior and siblings' prosocial behavior, respectively. The results are discussed in terms of their theoretical and prevention-related implications for children at risk for peer victimization.

The present study examined to what extent different types of friendship experiences (i.e., friendlessness, having depressed friends, and having nondepressed friends) are associated with early adolescents' longitudinal trajectories of depressed mood. On the basis of a sample of 201 youths (108 girls, 93 boys), we identified 3 distinct longitudinal profiles of depressed mood from Grade 5 (age 11) through Grade 7 (age 13): one group with consistently low levels of depressed mood, another group showing a sharp increase in depressed mood from late childhood through early adolescence, and a 3rd group with consistently high levels of depressed mood from late childhood through early adolescence. Subsequent analyses revealed that, compared to friendless youths, youths with nondepressed friends showed less elevated trajectories of depressed mood, whereas youths with depressed friends showed more elevated trajectories. The theoretical and practical implications of these findings are discussed.