The reward structure of a classroom refers to the means by which a teacher motivates students to perform school tasks. This document reports on a study in which academic achievement in competitive and reward-structured environments was examined in two high school sophomore level biology classes of equal academic ability. Each class was pretested and taught an identical unit of study, one in a competitive structure and one using a cooperative structure called the Group-Investigations Model. In this model groups of 5 or 6 students are formed for the study of a particular topic, and each student works on a subtopic for the group. At the end of 7 weeks both classes were post-tested. The results indicated that although both cooperative and competitive techniques obtained significantly higher post-test scores than their pre-test scores, neither strategy was superior to the other in producing academic achievement. Results are discussed and compared to previous studies which have examined differences between cooperatively, competitively, and individually structured classroom environments. (Author/TW)