This paper describes the implementation and effects of a behavior management system in eight middle schools, including control schools, in an urban school district. The components of the system included school discipline policy review and revision, computerized behavior tracking, classroom organization and management, and positive reinforcement. The components were implemented in the context of an organization development process designed to increase school staff commitment to the program. The treatment schools and control schools showed improvement over the 3-year project period, with greater improvement for the treatment schools, which reported significant effects on student reports of classroom order and organization, and clarity of rules. For the treatment schools, the extent of improvement corresponded to the strength of the implementation of the components. Nearly 40 references are cited. (RH)