The use of cooperative learning as an instructional procedure for delivering instruction has become popular among many educators. Research in cooperative learning has provided positive indicators for improvement in academic achievement and attitudes towards self, peers, and school. Little research has been performed on the type of students that compose these groups. The purpose of this study was to investigate the effects of homogeneous and heterogeneous ability created groups on individual student performance. Through the use of two problem solving activities, students were exposed to cooperative learning experiences followed by individual performance assessments. The two cooperative exercises provided varying results. No significant interaction effects were found in either case. The first exercise showed a significant main effect for ability level. Students in high ability groups overall scored higher than both middle and low ability groups, (F=6.78, p<.01). The second exercise produced significant main effects for cooperative type, ability level, and teacher. Homogeneous groups performed on the average at a higher level than heterogeneous groups (F=6.88, p<.01). Both high and middle grouped students scored higher than low ability students (F=13.85, p<.01). Teacher differences were present for this exercise (F=4.67, p<.01). / Ph. D.