We thank the many people who helped us with this project. Sarah Hansen helped with data analysis. Archer Larned, Chia hua Lue, Sarah Luttrell, Karan Odom, and Tory Williams implemented the modules and assessments and gave us a great deal of constructive feedback. Brian Dalton, Chia hua Lue, Michael Martin, and Tracy Smith were graduate students who developed much of the content of the modules. We are also grateful to our colleagues Tory Smith, Tamara Mendelson, and Kevin Omland, who supported the use of these modules in their courses. William LaCourse and Kathy Sutphin provided organizational support. We also thank our colleagues from the NEXUS project for advice, especially Kaci Thompson, Edward (Joe) Redish, Michael Gaines, Jane Indorf, Daniel DiResta, and Liliana Draghici. Special thanks to David Hanauer for his patient and incisive guidance on the assessment component of this project. This project was funded in part by a National Institutes of Health National Institute of General Medical Sciences grant (1T36GM078008) to Lasse Lindahl (UMBC), and an award from the HHMI to the UMBC under the Precollege and Undergraduate Science Training Program. Thanks to Tim Ford for help with the figures. We also thank two anonymous reviewers and Janet Batzli for helpful comments on the manuscript. All modules and course materials are freely available at http://nexus.umbc.edu or can be obtained by contacting the corresponding author.