The Responsive Math Teaching project has been developing and refining a model for the development of mathematics instructional leadership in a network of 13 urban under-resourced elementary schools. The project is a research-practice partnership with Learning Network 2 in the School District of Philadelphia, a city where more than 80% of students live below federal poverty levels in a state with some of the largest gaps in the country between wealthy and poor districts. The RMT project is built around five core components: Developing a shared understanding of high-quality math instruction Ongoing professional development Building a school culture of instructional improvement Leadership development for sustainability Ongoing research for continual improvement This report summarizes the core elements of this model for developing sustainable math instructional leadership for systemic change at the district level.