This report examines whether cooperative learning can be used to promote individual achievement, and identifies conditions under which a benefit can be expected. Two experiments were conducted at the Quartermaster School, Fort Lee, Virginia. The first experiment compared test performance of 280 trainees after they had completed practical exercises under either cooperative or individual learning. Results revealed that (1) cooperative learning improved individual trainee test scores but only when coupled with a group reward contingency, and (2) significant benefits occurred once group size reached four members. In the second experiment, 80 additional trainees were studied to determine why group reward was necessary for obtaining individual achievement benefits under cooperative learning. Two potential hypotheses were tested: that group reward effects were caused by increased individual trainee motivation to learn resulting from group pressure to perform, or that group reward encouraged groupmates to share information and that this "peer tutoring" facilitated individual learning. Test performance results supported the peer tutoring hypothesis. It was concluded that individual achievement gains can be obtained through cooperative learning in four-member groups without modifying training materials and without increasing the demand for training resources. (Author/JAZ)