Grounded in a close partnership between a university, school district, and non-profit organization, this 5-year mathematics professional development project involves 27 elementary teachers prepared and supported as Elementary Mathematics Specialists (EMSs). The project aims to develop EMSs who deliver ambitious mathematics instruction in their classrooms and serve as informal mathematics teacher leaders. They complete a university's K-5 Mathematics and Teacher Supporting & Coaching Endorsement programs and participate in Professional Learning Communities and individual mentoring. Described here are the partners, the project's components, and the ways in which the EMSs engaged in teacher leadership across Year 1. Central to the project is the school-university-community partnership, with the components supporting reciprocity with mutual benefits for all partners, such as high quality clinical experiences for teacher candidates, coaching for novice teachers, and engagement with families and caregivers.