This 5-year mathematics professional development project involves 27 elementary teachers being prepared and supported as Elementary Mathematics Specialists (EMSs) through completion of a university's K-5 Mathematics and Teacher Supporting & Coaching Endorsement programs, as well as participation in Professional Learning Communities and individual mentoring. Across the project, data are gathered to examine changes in mathematical content knowledge, instructional and coaching practices, beliefs, and teacher leader skills of the EMSs. Described here are Year 1 data from the participants, who have been identified as successful, experienced teachers, focusing on specific aspects of teacher effectiveness. The findings illuminate their classroom instructional practices, including those that are learner-centered and equitable, along with their early histories as learners of mathematics. [ABSTRACT FROM AUTHOR]