We studied the impact of cooperative learning on positive peer relationships, that is, liking to work together, in classroom networks. Cooperative learning was implemented as part of the "Success for All" program. Longitudinal social network analysis was used to investigate the development of structures and patterns of relationships in 16 intervention and 16 control classrooms, including a total of 791 students. Results showed significantly less reciprocation and transitivity in the dynamics of the intervention networks, while the number of nominations in the intervention classes was at least not smaller than in the control classes, indicating less tendency toward the formation of small clusters or cliques. We did not find that peer relationships became more diverse with regard to gender, socioeconomic status, or academic performance through the implementation of cooperative learning. In intervention classrooms, children tended to nominate their teammates with whom they work together in cooperative learning activities; however, also in control classrooms, children tended to nominate children with whom they are seated in the classroom. (PsycInfo Database Record (c) 2024 APA, all rights reserved).