In this study, the authors examined the extent to which children's self-regulation upon kindergarten entrance and classroom quality in kindergarten contributed to children's adaptive classroom behavior. Children's self-regulation was assessed using a direct assessment upon entrance into kindergarten. Classroom quality was measured on the basis of multiple classroom observations during the kindergarten year. Children's adaptive classroom behavior in kindergarten was assessed through teacher report and classroom observations: Teachers rated children's cognitive and behavioral self-control and work habits during the spring of the kindergarten year; observers rated children's engagement and measured off-task behavior at 2-month intervals from November to May. Hierarchical linear models revealed that children's self-regulation upon school entry in a direct assessment related to teachers' report of behavioral self-control, cognitive self-control, and work habits in the spring of the kindergarten year. Classroom quality, particularly teachers' effective classroom management, was linked to children's greater behavioral and cognitive self-control, children's higher behavioral engagement, and less time spent off-task in the classroom. Classroom quality did not moderate the relation between children's self-regulation upon school entry and children's adaptive classroom behaviors in kindergarten. The discussion considers the implications of classroom management for supporting children's early development of behavioral skills that are important in school settings.