Teaching mathematics to diverse learners can be a challenge. The extensive and specialized knowledge that special education teachers need to possess to be considered high-quality teachers is often lacking in preservice and inservice education, yet is mandated by current teacher reforms and rigorous measures of accountability. To provide direction for supporting teacher growth in these areas, this article highlights four knowledge bases that special education teachers should develop and expand upon as a way to improve their instruction for diverse learners in mathematics. Numerous resources and materials are provided to support the development of teacher expertise in content, characteristics of diverse learners, technology, and pedagogy.