This investigation examines the extent to which characteristics of the teacher-child relationship (closeness, dependency, and conflict) are predictive of changes in children's peer victimization and aggressive behavior over the course of a school year. Relational and physical forms of victimization and aggression were studied, and changes in peer acceptance and number of friendships were tested as possible mediators. Longitudinal data from 410 fourth- and fifth-grade students (193 boys; 217 girls) and their teachers (N = 25) were analyzed. Whereas dependency on the teacher predicted heightened victimization from peers, a close relationship with the teacher forecasted less physical aggression toward peers. Moreover, decreases in number of friendships partially mediated the link between dependency on the teacher and heightened relational victimization for boys. These findings have implications for understanding the continuing influence of teacher-child relationships on children's social development in late childhood and for identifying interpersonal risk factors associated with involvement in peer harassment.