This paper describes the role of the school-based mathematics specialist of the Project IMPACT (Increasing the Mathematical Power or All Children and Teachers) whose primary purpose is to design, implement, and evaluate a model for primary mathematics instruction that will enhance student understanding and support teacher change in predominantly minority schools. The program is described followed by a description of the selection and role of the mathematics specialist. The supportive interaction among specialists and with classroom teachers is discussed, including excerpts from specialists' journal writings to indicate both the nature of and the need for specialist-teacher interactions. Concluding the paper is a list of recommendations for encouraging teacher change. (MKR)