The recent NRC report emphasizes the important role that school leaders play in promoting and supporting STEM learning in their schools. They play a role in setting a vision for STEM learning and teaching, identifying and hiring highly qualified teachers, providing and/or identifying relevant professional development opportunities, and establishing and sustaining school structures that support high-quality instruction. EDC has been engaged in a long-standing program of research and development aimed at understanding the nature of “leadership content knowledge” in mathematics in school principals, and in creating professional development supports for principals and other school and district leaders to help them improve STEM learning. The core set of materials consist of Lenses on Learning professional development programs designed to support K–12 principals, teacher leaders, and district leaders to develop their instructional leadership by focusing on issues of equity, assessment, data use, and high-quality mathematics instruction. A number of districts and educational organizations have trained Lenses on Learning facilitators who offer professional development courses for administrators and district leaders as well as facilitator training institutes. In addition, the Lenses on Learning materials have been adapted for use in other programs that take a broader, systemic view on STEM learning and teaching. The development of the Lenses on Learning professional development materials was based on years of research about administrators’ knowledge about mathematics instruction and their professional practice supporting and supervising mathematics instruction in their schools. Although the Lenses on Learning materials predate the Common Core State Standards, they were designed around the same mathematical processes and proficiencies.