This study aimed to understand how relationships with peers and teachers contribute to the development of internalizing problems via children's social self‐concept. The sample included 570 children aged 7 years 5 months (SD = 4.6 months). Peer nominations of peer rejection, child‐reported social self‐concept, and teacher‐reported internalizing problems were assessed longitudinally in the fall and spring of Grades 2 and 3. Teacher reports of support to the child were assessed in Grade 2. Results showed that peer rejection impeded children's social self‐concept, which in turn affected the development of internalizing problems. Partial support was found for individual (but not classroom‐level) teacher support to buffer the adverse effects of peer problems on children's self‐concept, thereby mitigating its indirect effects on internalizing problems.