This research investigated the role of children's implicit theories of peer relationships in their psychological, emotional, and behavioral adjustment. Participants included 206 children (110 girls; 96 boys; M age = 10.13 years, SD = 1.16) who reported on their implicit theories of peer relationships, social goal orientation, need for approval, depressive and aggressive symptoms, and exposure to peer victimization. Parents also provided reports on aggressive symptoms. Results confirmed that holding an entity theory of peer relationships was associated with a greater tendency to endorse performance-oriented social goals and to evaluate oneself negatively in the face of peer disapproval. Moreover, entity theorists were more likely than incremental theorists to demonstrate depressive and aggressive symptoms when victimized. These findings contribute to social-cognitive theories of motivation and personality, and have practical implications for children exposed to peer victimization and associated difficulties.