Esther Mertens

92 | Chapter 5 Abstract Experiences with classmates can affect adolescents’ academic, emotional, and social development. We examined whether classmates’ modeling and reinforcement were mechanisms of change in an intervention addressing the classroom peer context. Additionally, we examined whether relations between classmates’ modeling and reinforcement and the perceived classroom peer context were moderated by dyadic mutuality. Questionnaires and observations were used in a sample of 7 th Grade students ( N = 160; M age  = 12.37; 53.8% boys). Classmates’ modeling and reinforcement were not mechanisms of change. An increase in prosocial modeling, though, was related to a decrease in victimization, especially for dyads with high levels of mutuality. The results suggest that interventions should specifically focus on improving prosocial modeling and dyadic mutuality between classmates. This trial is preregistered in the Dutch Trial Register, number NL6371 (NTR6554), registered on the 3rd of July 2017. Keywords: peer influence; school-based intervention; perceived classroom peer context; dyadic mutuality; modeling; reinforcement