This research was supported by grant 52008126 from the Howard Hughes Medical Institute to the University of Washington and a grant from the University of Washington’s College of Arts and Sciences, Office of the Dean. We thank John Parks for logistical support and advice, Elinore Theobald for guidance on statistical analyses, and the instructional staff of both courses. For comments that improved the article, we thank the Biology Education Research Group at the University of Washington and three anonymous reviewers.