The investigators propose to integrate a few simple, flexible, and powerful prevention strategies that have proven value in establishing a social context conducive to positive peer group development. This project will apply cooperative learning and behavioral kernels to reduce social rejection and isolation, promote new friendships among youth from different social groups, and encourage greater levels of prosocial behavior. This should create a positive feedback loop in which the social and behavioral processes "amplify" one another to bring significant change to the school social context, interrupting deviant peer clustering and addressing a key root cause of escalations in substance use and related problem behavior. With this approach, the investigators anticipate a simple, straightforward implementation, greater sustainability, and opportunities for the program to spread through sharing of best practices among teachers. This project will conduct a small-scale randomized controlled trial involving 12 middle schools in the state of Oregon.