One of the most promising developments in math education is the fact that many districts are hiring math coaches--also called math resource teachers, math facilitators, math lead teachers, or math specialists--to assist elementary-level teachers with math instruction. What must not be lost, however, is that principals play an essential role in supporting math coaches' work. The Boston Public Schools is in its ninth year of a math plan that includes teachers using a standards-based math curriculum, a comprehensive program of professional development for teachers and administrators, a system of formative assessments designed to monitor and inform instruction, and school-based support from math coaches. Principals play a key role in supporting these efforts, particularly when it comes to taking full advantage of what a math coach might offer. This article offers four important ways in which a principal can partner with a math coach. (Contains 2 online resources.)