This study describes the process by which a statewide support system was developed in Maryland to promote high-quality implementation of a school-wide prevention model called Positive Behavioral Interventions and Supports (PBIS). PBIS (Sugai & Horner, 2006) aims to prevent disruptive behavior problems and promote a positive school climate through the application of practices and systems consistent with the three-tiered public health prevention framework. We summarize the statewide scale-up process and examine school and district-level contextual factors that influenced the schools' training, adoption, and implementation quality of PBIS within the scale-up effort. Data come from 810 Maryland elementary schools, of which 316 were trained in PBIS. A series of multilevel analyses indicated that several school- and district-level factors were associated with both receipt of training and program adoption; however, only school-level factors were related to implementation quality. Findings are discussed within the context of statewide efforts to scale up evidence-based programs in schools. (Contains 3 tables.)