This dissertation aimed to advance the field of biology education in several ways. First, we aimed to demonstrate if, and to what extent, student-generated conceptual models can be used on summative assessments to accurately assess student understanding of gene expression. Next, we described patterns of changes students make to conceptual models of gene expression during a formative revision process aimed to prepare students for summative modeling tasks. Next, we analyzed reflections students created during the model revision process to provide insight into students' reasoning behind the changes they make during the revision process. Also, following instructor feedback, we described the changes students made and the accuracy before and after the feedback was given. Finally, a summary of the main findings from the data chapters and additional commentary is discussed. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]