This study used an observational measure to examine how individual children's engagement with teachers, peers, and tasks was associated with gains in self-regulation. A sample of 341 preschoolers was observed, and direct assessments and teacher reports of self-regulation were obtained in the fall and spring of the preschool year. Research Findings: Children's positive engagement with teachers was related to gains in compliance/executive function, and children's active engagement with tasks was associated with gains in emotion regulation across the year. Engaging positively with teachers or peers was especially supportive of children's gains in task orientation and reductions in dysregulation. Practice or Policy: Results are discussed in relation to Vygotsky's developmental theory, emphasizing that psychological processes are developed in the context of socially embedded interactions. Systematically observing how a child interacts with peers, teachers, and learning tasks in the preschool classroom has the potential to inform the creation of professional development aimed at supporting teachers in fostering individual children's development within the early education environment. (Contains 3 tables and 2 figures.)