Although kindergarteners often are excited to share their mathematical ideas, they may not be sure how to explain the underlying reasoning that brought them to their answers. Teachers seeking to use literacy skills in mathematics to support kindergarteners' reasoning can use writing to provide each student an avenue to communicate their individual reasoning. Writing further broadens students' ways of communicating mathematically because this medium incorporates representations, including drawings, which are typical ways young students share their ideas. Developing writing during mathematics class has the potential to provide more insights into students' depth of understanding of the content while advancing key literacy skills. This article shares an approach to introducing and supporting kindergarteners in learning to write mathematically. The article then describes implementation and reflections. Finally, the authors share their plans for continuing this work based on their observations across the implementation.