Math for America Los Angeles (MfA LA) is a non-profit organization formed by the University of Southern California (USC), Claremont Graduate University (CGU) and Harvey Mudd College (HMC) whose mission is to raise student achievement by addressing issues of teacher recruitment, retention and quality in the greater Los Angeles area. In concert with current efforts to recruit talented new secondary mathematics teachers through the MfA LA Teacher Fellowship Program, MfA LA is developing a cadre of 24 experienced mathematics teacher leaders. Because of chronic shortages in qualified mathematics teachers in California and the high cost of recruiting and training teachers due to teacher attrition, it is critical to ensure that the most talented teachers do not leave the profession, but instead find avenues for professional growth. MfA LA has designed a novel, research-based program to give passionate teachers a comprehensive package of training, resources, professional development experiences and connections to become leaders who can enact school change and raise student performance. A key idea of the MfA LAMaster Teaching Fellowship Program (MTFP) is that there is no better way for teachers to develop their leadership capacity than to directly engage them in the work of designing and orchestrating student-centered changes in their schools and districts, with the support of other experienced teachers and STEM educators. Pairs of teachers who work at the same school apply to the program, and if selected, must agree to participate in the program together for at least five years during which time they receive a $10,000 annual stipend, receive training in mentoring, mentor beginning teachers, participate in the three-week Park City Mathematics Institute Secondary School Teachers Program, receive mentoring and support from local STEM faculty and other Master Teachers through regular professional development meetings, present their work at regional or national mathematics education conferences, and receive training and support to become certified by the National Board of Professional Teaching Standards. In total, this Master Teacher Fellowship Program includes roughly 300 hours of professional development over five years. Assuming that one teacher reaches 200 students a year, the 24 MfA LA Master Teachers can directly reach 24,000 students over five years of service while bringing about systemic changes in their schools and districts to improve student performance and helping their colleagues and other beginning teachers improve their practice.