The effects of a form of cooperative group instruction called Team Assisted Individualization on students in a high school Algebra II class were examined. Sixty-two (31 female and 31 male) 11th-grade students were randomly assigned to either a cooperative learning (32 students) or traditional lecture (30 students) group. Students completed an instrument that assessed efficacy, intrinsic valuing, and goal orientation on 3 occasions: at the beginning of the school term, after the first 18 weeks of the project, and at the end of the school term. Algebra achievement was assessed at the same times using teacher-made examinations. Students in the cooperative classroom exhibited significantly higher gains than did the control group in algebra achievement, efficacy, intrinsic valuing of algebra, and learning goal orientation. Surprisingly, the achievement and motivational gains were completely reversed when the cooperative class was switched to traditional instruction for the last 18 weeks of the project. The implications of these findings for motivational theory and cooperative group structures are discussed. Four tables present study data. (Author/SLD)