Research Findings: This study aims to understand the ways in which classroom-level teacher-child interaction quality is predictive of self-regulatory behavior and physiology. Specifically, we examine if high-quality and consistent behavioral and emotional support are related to preschool children's behavioral self-regulation, inhibitory control, and morning cortisol levels at child care. Fifty-four children within 11 center-based preschool classrooms participated. Saliva was collected at child care over two mornings and assayed for cortisol; two direct assessments of self-regulation were conducted. Classroom quality was observed over two days with the Classroom Assessment Scoring System. Models predicting self-regulation find that high-quality Emotional Support predicted higher behavioral self-regulation and inhibitory control skills for preschool children. No significant associations with consistency of teacher-child interactions emerged; however, there was a trend-level association between consistently managed classrooms and behavioral self-regulation. Results indicate no association between classroom-level interaction quality or consistency and children's cortisol at child care. Practice or Policy: Our findings indicate that classroom-level, emotionally supportive interactions predict higher behavioral self-regulation and inhibitory control for preschool children. Thus, teachers who foster relationships in the classroom that are supportive and responsive may help to support preschool children's self-regulation skills.