In recent years, national organizations, mathematics educators, and policy makers have called for the development of elementary school mathematics coaches to improve mathematics teaching and learning in elementary schools. The literacy field has found success and promise in the work of instructional coaches, and the mathematics education community can benefit from what professionals in literacy have learned and practiced. This article presents a synthesis of empirical research about instructional coaches, in both literacy and mathematics, as well as the neo-Vygotskian construct of assisted performance. Following the synthesis, implications are presented regarding how to develop the essential skills and knowledge needed for elementary school mathematics coaches as well as how to examine the impact of their efforts in schools.