We examine preservice mathematics teachers' conceptions of writing as a tool for learning mathematics before and after participation in and reflection on writing tasks. We describe the use of two targeted activities incorporated into a secondary methods course: writing to learn mathematics (WTLM) and reflection on that writing. Prior to participation in these activities, the preservice teachers expressed reluctance toward the use of writing in mathematics and uncertainty as to how writing could be useful in mathematics, while accepting that some possible benefits might exist for students' procedural learning. Following participation in these activities, the preservice teachers expressed a willingness to accept writing as a useful tool for supporting an expanded view of teaching and learning mathematics. Specifically, the preservice teachers considered writing as a way to build connections between mathematics and other subjects, a means to assess student understanding of mathematics, and a beneficial support for student conceptual learning.