Despite research demonstrating positive effects of writing on student achievement, writing-to-learn remains under-utilised in mathematics and mathematics teacher education. In this paper, we explore how writing-to-learn tasks in a mathematics methods course influenced elementary preservice teachers' beliefs about teaching in two domains: mathematics "and" writing. Preservice teachers engaged in weekly writing-to-learn tasks designed to support their understanding of mathematics content and mathematics pedagogy over the course of a semester. Using survey data, we found no significant difference in their beliefs from pre to post. Such null findings led us to ask new qualitative questions, resulting in a concurrent mixed methods design. Through qualitative analyses of student writing, we found several meaningful and non-meaningful practices for engaging in writing-to-learn tasks. This research supports teacher educators, teachers, and researchers to understand how to implement writing-to-learn tasks and to support students towards meaningful engagement in the tasks.