Using argument writing to enhance students' mathematics learning has been shown to increase students' content knowledge. Investigating argument writing has also been found to increase the content knowledge and quality of mathematical reasoning of students with learning challenges. This chapter examines the instructional challenges for implementing mathematics writing to students who experience learning difficulties, evidence-based practices to address these students' math and writing needs, and a closer look at how constructing written arguments can enhance fraction knowledge and genre knowledge for students with learning difficulties.