Based on attachment theory, we tested whether the link between dyadic teacher–child interactions and task engagement operates through a child's security with the teacher. In a sample of preschoolers (N = 470) rated by their teachers as exhibiting elevated disruptive behaviors, the quality of dyadic teacher– child interactions and children's security were observed using a standardized task. Children's engagement with tasks was both observed in the preschool classroom and rated by the teacher. Results indicated that the quality of teacher–child dyadic interactions was associated directly with teacher‐reported task engagement, and indirectly associated, through a child's security, with observed task engagement. We discussed the contribution of these findings to our understanding of how the quality of dyadic teacher–child interactions may serve to regulate children's behavior in the classroom for children whose teachers perceive them as displaying early externalizing behaviors. (author abstract)