This study evaluated the effectiveness of Jigsaw as a strategy to prevent substance abuse. Jigsaw is a structered peer teaching program in which students teach part of the regular classroom curriculum to a group of peers. The goals of Jigsaw were to make student learning more active and student-student interactions more cooperative. As a result of these changes, students were expected to develop more positive attitudes, behaviors and norms regarding self, peers and school. Eventually, these gains should reduce students' acceptance and use of psychoactive substances. The treatment group consisted of 13 fourth-sixth grade teachers and their 261 students. Thirty teachers and their 560 students served as the nonparticipant comparison group. The Jigsaw in-service training consisted of two-hour sessions, held once a week for nine weeks, and one review session held six weeks later. The trainer assisted teachers in their classrooms both before and after the training ended. Participant and nonparticipant teachers and students were pre- and post-tested and data regarding achievement and attendance were gathered from school district records. Teachers also rated their students' classroom behavior. (Author/CE)