Although there is an established literature supporting the efficacy of a variety of prevention programs, there has been less empirical work on the translation of such research to everyday practice or when scaled-up state-wide. There is a considerable need for more research on factors that enhance implementation of programs and optimize outcomes, particularly in school settings. The current paper examines how the implementation fidelity of an increasingly popular and widely disseminated prevention model called, School-wide Positive Behavioral Interventions and Supports (SW-PBIS), relates to student outcomes within the context of a state-wide scale-up effort. Data come from a scale-up effort of SW-PBIS in Maryland; the sample included 421 elementary and middle schools trained in SW-PBIS. SW-PBIS fidelity, as measured by one of three fidelity measures, was found to be associated with higher math achievement, higher reading achievement, and lower truancy. School contextual factors were related to implementation levels and outcomes. Implications for scale-up efforts of behavioral and mental health interventions and measurement considerations are discussed.