We conducted a study to examine how a writing-to-learn assignment influenced student learning of polymer behavior. In particular, we examined the role of specific content and a rhetorical framework as well as a structured writing process including peer review and revision. The student-generated writing was analyzed via a content-directed rubric. Students' conceptual understanding of stress-strain behavior was gauged via a multitiered assessment. Finally, interviews were conducted to probe students' experiences during the writing process. Results indicate that the writing-to-learn assignment was effective in promoting understanding of stress-strain properties, but that further support is needed to help students connect polymer microscopic properties to macroscopic behavior. Specifically, the content requirements and rhetorical framework guided what students included in their writing. Peer review and revision provided students with further opportunities to engage and learn the material.