The Support Teacher Program is a professional development program created to increase teachers' mathematical knowledge, improve instructional practices for conceptual understanding, and prepare teachers to conduct staff development activities in their schools with their colleagues. This paper is presented in three sections. The first section includes a description of this staff development model, the program goals, a description of the framework for guiding instructional and curricular changes, and the activities of the mathematics Support Teachers. The second section examines the impact of the program on the quality of mathematics instruction of three junior high school teachers who participated in the program. Data was gathered from the Teaching Style inventory, the Support Teacher Interview, and documentation of the Support Teachers' mathematics curriculum. Results indicated: (1) Each Support Teacher's thoughts and practices changed as a result of the program; (2) Support Teachers were adequately prepared for their new role by increasing their knowledge of and experience in effective instructional strategies and support techniques; (3) Teaching colleagues of the Support Teachers were influenced in varying degrees; and (4) Student results at the end of the first year indicated a more positive attitude towards mathematics, an improved ability to solve problems, and increased conceptual understanding. The third section includes comments on the Support Teacher Program. An appendix includes the Mathematics Support Teacher Reading List. (Contains 26 references.) (MDH)