Young children with and at risk for emotional/behavioral disorders (EBD) present challenges for early childhood teachers. Evidence-based programs designed to address these young children's behavior problems exist, but there are a number of barriers to implementing these programs in early childhood settings. Advancing the science of treatment integrity measurement can assist researchers and consumers interested in implementing evidence-based programs in early childhood classrooms. To provide guidance for researchers interested in assessing the integrity of implementation efforts, we describe a conceptual model of implementation of evidence-based programs designed to prevent EBD when applied in early childhood settings. Next, we describe steps that can be used to develop treatment integrity measures. Last, we discuss factors to consider when developing treatment integrity measures with specific emphasis on psychometrically strong measures that have maximum utility for implementation research in early childhood classrooms. [This article was published in "Journal of Early Intervention," (EJ1019931).]