Young adolescents spend the majority of their time in school, yet little is known about how the school context is associated with their prosocial conduct. The current study focused on 1) the extent to which individual students were teamed with their classmates and 2) their exposure to ethnically diverse peers, and examined the processes by which these aspects of the school context were associated with their prosocial conduct. Multilevel mediation models were fit to multiply imputed questionnaire data collected from a sample of 3,738 sixth grade students from 19 ethnically diverse urban middle schools in California.

A novel teaming index that captured the extent to which individual students shared academic classes with classmates was used to test the first mediation hypothesis. It was expected that students who were extensively teamed would feel a stronger sense of school belonging and perceive prosocial behaviors to be more normative among their grade mates, which in turn were expected to be associated with more frequent prosocial conduct. Although no evidence of mediation was found, both sense of school belonging and perceptions of prosocial norms were positively and significantly associated with more frequent prosocial conduct.

The novel application of Simpson's diversity index to assess individual students' exposure to ethnic diversity was used to test the second mediation hypothesis. It was expected that students who had greater exposure to ethnic diversity in their classes would report a stronger sense of safety at school and have a greater proportion of cross-ethnic friendships, which in turn were expected to be associated with more frequent prosocial conduct. While the indirect effect of sense of safety was significant, the indirect effect of proportion of cross-ethnic friendships was only marginally significant.

Together, findings suggested that the ways in which students perceive and experience the school context are linked to their prosocial conduct with peers. Findings from the first mediation model suggested that seeing the same classmates in many courses may not be enough to support feelings of belonging or perceptions of prosocial norms. However, students' sense of school belonging and perceptions of prosocial norms were related to their prosocial behavior. The findings from the second mediation model, in turn, indicated that exposure to ethnically diverse peers across classes is associated with a sense of safety that may facilitate engagement in prosocial conduct. The results also suggested that the cross-ethnic friendships afforded by ethnically diverse classrooms are associated with students' tendency to extend kind and helpful gestures to their peers. Contributions of the novel indices used and implications of the present findings on educational research and practice are discussed.