Much evidence supports the role of writing-to-learn (WTL) assignments in improving student learning and argumentation skills. However, designing effective assignments can be challenging for instructors. We describe a process for modifying WTL assignments that were originally developed for small undergraduate biology classes (24 students) for use in large introductory cell biology courses (>80 students). Students explore a socioscientific issue (cancer treatment) intended to engage them. Students learn content through reading journal articles and textbook chapters, attending class, and participating in discussions. All along, students participate in iterative writing assignments and engage in peer evaluation and self-evaluation. Finally, students write persuasive arguments about how best to treat cancer. We describe how instructors can develop their own WTL assignments in their large biology courses.