Elementary school teachers in Seattle, Washington, are encouraged to adapt differentiated instructional practices in math to accommodate the particular students in their own classrooms. Seattle Public Schools is a large, urban district serving 47,000 students who speak over a hundred languages. More than a third receive free or reduced lunch. The Everyday Mathematics curriculum developed by the University of Chicago School Mathematics Project has been the core math program for the district's elementary schools since 2007. During the 2008-2011 school years, the district funded a sizable cadre of school-based math coaches who coordinated with district-based math coaches. Differentiated instructional practices began to spread throughout classrooms in the district, not because the district imposed a predetermined instructional practice but because coaches facilitated teachers in learning from one another's differentiated practices. Being in classrooms daily, math coaches noticed some effective settings in which students of all achievement levels--including those who traditionally had not been successful--were making great strides in mastering math. The teachers in these classrooms had developed their own strategies for differentiating math instruction so that every student was supported in progressing from his or her present level of understanding to a much higher level. Because coaches from across the district met regularly to share and learn from one another, news of these teachers spread throughout the coaching cadre and then to teachers in schools that had math coaches. This article focuses on two classrooms that spurred much of the differentiation throughout the district and how the district supported teachers' efforts.