This study tests the predictive associations between externalizing behaviors and internalizing symptoms and examines the mediating roles of social competence, parent-child conflicts, and academic achievement. Using youth-, parent-, and teacher-reported longitudinal data on a sample of 523 boys and 460 girls from late childhood to early adolescence, we found evidence for pathways between externalizing behaviors and internalizing symptoms in both directions. Parent-child conflict, but not social competence and academic achievement, was found to be a significant mediator such that externalizing behaviors predicted parent-child conflicts, which in turn, predicted internalizing symptoms. Internalizing symptoms showed more continuity during early adolescence for girls than boys. For boys, academic achievement was unexpectedly, positively predictive of internalizing symptoms. The results highlight the importance of facilitating positive parental and caregiver involvement during adolescence in alleviating the risk of co-occurring psychopathology.