To provide insight into the strengths and limitations of using groupwork to promote excellence and equity in science education, the researcher investigated how students using the Complex Instruction model of groupwork constructed scientific knowledge. Eighty sixth-grade students and one life science teacher at an urban middle school participated in this study. Qualitative analysis of videotapes and interviews makes clear that group discussions rarely moved beyond observational or procedural matters, that students of high status (perceived academic ability and popularity) had greater access to their groups' materials and discourse, and that students made few connections among the contexts of school, science, and everyday life. Quantitative analyses of participation during groupwork and performance on unit tests show that high-status students had significantly higher rates of on-task talk than their middle- or low-status counterparts, and that those students who talked more learned more as well. Thus, although groupwork should not be summarily dismissed as an instructional strategy, group tasks and implementation must be further refined to adequately address the dual goals of excellence and equity: Students need greater guidance in how to talk and do science, and teachers, greater assistance in eliminating differences in student participation and achievement. © 1997 John Wiley & Sons, Inc. J Res Sci Teach 34: 1039–1065, 1997.