Achievement in individually competitive and cooperatively reward-structured environments was examined in two high-school biology classrooms. Each was pretested and taught an identical unit of study, one in an individually competitive structure and the other using a cooperative group-investigation model. At the end of seven weeks both classes were posttested. A two-way within-subjects ANOVA was used to determine significant differences in pre- and post-test scores between the two treatment groups. The two groups were not significantly different from each other on the pretest. While both cooperative and competitive techniques obtained significantly (p < 0.05) higher posttest scores, neither treatment was superior over the other in producing academic achievement. Results are compared to previous studies which have examined differences among cooperatively, competitively, and individually structured classrooms.