This action research project investigated the effects of music on the behavior and performance of students (ages 3-21) with multiple disabilities, mental retardation, or severe mental retardation in four self-contained special education classrooms. The teacher researchers involved in the study made no assumptions with regard to the outcomes. It was hoped that music would provide a variety of positive outcomes on students' learning and attitudes, a calming effect on students with mercurial behaviors, an energizing effect on students with low affect, a reduction of disruptive self-stimulatory behavior, and an increased ability to focus on a task. The intervention involved playing the music to alter the climate of the classroom. Music was an additional component to regular classroom procedures. Data collection included anecdotal records, direct teacher observation, and student interviews. In all four classrooms, music proved itself to be a powerful tool in altering student behavior. A reduction was observed in volume of the participants' voices. Out of seat behavior decreased. In a single case, there was a light reduction in self-stimulatory behavior. The teachers involved in the study will continue to use classical, 60 beat per minute selections during various activities. (Contains 37 references.) (Author/CR)