This investigation examined the effects of a classroom-based intervention, Behavioral, Emotional, and Social Training: Competent Learners Achieving School Success (BEST in CLASS), on teacher behaviors and child outcomes in early childhood classrooms. First, we examined the effects of professional development training and practice-based coaching (including performance feedback) on teachers’ implementation and maintenance of the BEST in CLASS model practices. Next, we examined the effects of teachers’ implementation of these practices on young children’s engagement and problem behaviors. Using a descriptive nonexperimental design, 10 teachers and 19 children received the intervention. Findings indicated that teachers’ use of the BEST in CLASS practices including rules, precorrection, opportunities to respond, behavior-specific praise, and instructive and corrective feedback increased from baseline to completion of the intervention and these increases maintained. In addition, children’s engagement increased while their problem behaviors decreased. Although these results are promising, the current investigation has limitations and the results should be viewed with caution.