As science teachers at a suburban California high school, the authors were concerned about the lab report conclusions written by their upper-level chemistry, biology, and ecology students--which were consistently of poor quality. Their work lacked inferences derived from data and support for their concluding statements. Working as part of a collaborative project with the University of California at Davis, they formed a teacher research group to investigate this matter. This article describes the group's efforts and its implications for the classroom. (Contains 5 figures.)