This study did not collect data on instruction. Clearly, many other factors besides teacher knowledge affect student learning. Among these, the project provided all teachers with instructional materials for teaching a unit on force and motion. Many aspects of these materials are educative for the teachers. As such, it is likely that the materials compensated for some gaps in teacher content knowledge. If that is the case, then this study probably underestimates the relationship between teacher knowledge (as measured by the ATLAST assessment) and student learning.