The goals of this study were to examine the additive and interactive effects of cumulative risk and child negative emotionality on children's social competence in the transition from preschool to school and to test whether these associations were mediated by child emotion regulation within a sample of 310 low‐income, ethnically diverse boys. Multiple informants and methods were used to measure contextual risk factors and negative emotionality at the ages of 1.5 and two, emotion dysregulation at the age of 3.5, and social competence in the home at the age of five and in school at the age of six. Results indicated that the relation between cumulative risk and emotion dysregulation was amplified for children with higher levels of negative emotionality. In turn, emotion dysregulation predicted lower social competence across both the home and the school contexts. This study represents an early effort to develop an integrative model of social competence by considering joint contributions of contextual risk, negative emotionality, and emotion regulation.