This article describes a major capstone course centered on public writing, whose underlying pedagogical principles are transferable to courses across the curriculum. The course aims to strengthen students' mathematical agency and their ability to effectively communicate mathematical ideas. In its unique format, students repeatedly take turns writing articles aimed at a variety of audiences and editing peers' work. Student reflections and survey data demonstrate that this collaborative, active format builds students' confidence in math and writing and their sense of belonging in the mathematical community. The last section offers suggestions for getting started with implementing aspects of this pedagogy.