Cooperative group learning involves organizing students in small heterogeneous groups to work on academic assignments. This paper reports a staff development project to implement cooperative group learning for 417 general education middle school and junior high school students, including 41 special education students. To impart cooperative learning skills, a cooperative approach to staff development was used, including teacher support teams, teacher decision-making, and peer coaching. Teachers were involved in project-related decisions on format, class content, and training session schedules. By the end of the year, students in cooperative classes experienced greater decreases in alienation or feelings of estrangement from school, peers, and classroom activities than students in control classes. They also experienced greater feelings of positive interdependence with their classmates than students in control or contrast classes. Special education students in cooperative classes were rated more favorably over the year by their regular class peers; non-handicapped students in cooperative classes also rated one another more positively than students in contrast classes. Teachers were using cooperative learning procedures from 25% to 50% of the time in their classes by the end of the year. They evaluated the project favorably. (DHP)