The purpose of this paper is to report a successful technique for assessing cooperative group work reliably and validly. The paper demonstrates a simple-to-use assessment procedure that tracks individual accountability, energizes student interaction, and rewards cooperative learning, even as it uses fewer administrative resources than traditional approaches. The difficulty in assessing an individual's contribution to group work lies in determining who did what. The solution suggested here is to separate the assessment of the final product from the assessment of each individual's contribution. In practice, students are given the criteria for the final product at the beginning of the work, and they receive a confidential feedback sheet on which they make a judgment about the percentage of each member's contribution to the group work, including their own if that assessment is culturally appropriate. These forms are confidential and not anonymous. The form also asks for the rationale for each judgment. Percentages awarded by each group member are averaged, and this average is applied to the product of the independently awarded product score times the number of members of the group. Students are not asked to assess the quality of the work, but only the contributions of each group member. (Contains 1 table and 10 references.) (SLD)