How the interplay between peer relationships and behaviors unfolds and how this differs between classrooms is an understudied topic. This study examined whether adolescents befriend or dislike peers whom they consider as aggressor or victim and whether these results differ in classrooms that received an intervention to promote prosocial behavior compared to classrooms without the intervention. The sample was composed of 659 seventh graders (M-age = 12.32; 48% girls) from nine intervention and seven control classrooms in eight schools in Santiago, Chile. It was hypothesized that adolescents in intervention classrooms would be less befriended and more disliked by classmates who considered them as aggressors, and more befriended and less disliked by classmates who considered them as victims, compared to control classrooms. Longitudinal multiplex social network analyses (RSiena) indicate that antipathies toward peers considered as aggressive and victimized were significantly lower in intervention classrooms than in control classrooms, but no significant differences were found for friendships. These findings suggest that the impact of an educational intervention may go beyond changing individual behavior and extend to the way peer relations develop in classrooms.