In the longitudinal study presented here, we tested the theoretical assumption that children�s task-focused behavior in learning situations mediates the associations between supportive interpersonal environments and academic performance. The sample consisted of 2,137 Finnish-speaking children. Data on supportive interpersonal environments (characterized by authoritative parenting, positive teacher affect toward the child, and peer acceptance) were gathered in Grade 1. The children�s task-focused behavior was measured in Grades 2 and 3, and academic performance was measured in Grades 1 and 4. The results supported our assumption by showing that all three supportive environments were positively associated with children�s subsequent academic performance via increased task-focused behavior in learning situations. These findings suggest that students� academic performance can be promoted by increasing the support they receive from peers, parents, and teachers because such increased support leads to better task focus in learning tasks.