The existing scientific literature strongly suggests that the most effective interventions for children and youth typically require active implementation of treatment in their natural environments by in-vivo care providers. These findings align with the practice of applied behavior analysis. Research over the last two decades in particular has demonstrated that simply providing care providers verbal directions is frequently insufficient to assure treatment implementation. This session will focus on findings relevant to assuring implementation of intervention plans in the natural environment with a particular focus on teachers as the treatment agents. The session will describe conceptual issues surrounding the assessment and assurance of treatment integrity in applied settings. Additionally, the session will review findings regarding procedures that have been found to be effective across studies in supporting intervention implementation as well as often repeated hypotheses about factors mediating treatment implementation that have not been supported by data. The session will conclude with a focus on future directions and the application of a behavior analytic science of treatment implementation across contexts.