The primary purpose of this paper is to review how BEST in CLASS, an evidence-based program targeting children at risk for emotional and behavior disorders, interacts with a diverse range of social ecological factors to promote successful implementation. Recent findings from two BEST in CLASS studies (BEST in CLASS-Prekindergarten and BEST in CLASS- Elementary) are reviewed in relation to barriers and facilitators of high quality implementation. The importance of taking into account factors associated with teacher delivery of interventions in classrooms, particularly for children with and at-risk for emotional and behavioral disorders, when designing and evaluating interventions is discussed. Implications for future research and practice are provided. [For the Grantee Submission, see ED608948.]