The measurement of treatment integrity is critical to evaluate the efficacy and effectiveness of evidence-based programs (EBPs) designed to improve the developmental outcomes of young children at risk of emotional/behavioral disorders. Unfortunately, the science of treatment integrity measurement lags behind the development and evaluation of EBP for young, high-risk children. This article describes the development and preliminary psychometric properties of the BEST in CLASS Adherence and Competence Scale (BiCACS), designed to measure the adherence and competence of delivery of the BEST in CLASS prevention program. Independent observers coded videotaped (n = 116) and live (n = 289) observations of teachers delivering the BEST in CLASS program. The BiCACS showed good interrater reliability and analyses provided some support for the validity of the measure. Implications for future research and integrity measurement work are discussed. (author abstract)