While elementary school teachers want their students to be better mathematical thinkers, their own teaching styles too often inhibit reflection and interpretation. The goal of the proposed project is to generate more and better mathematical discourse in elementary classrooms by helping teachers talk mathematics with their students. Over the course of this eighteen month project, Technical Education Research Centers will work with mathematicians, mathematics educators, and 10-12 teachers from several school districts to identify the difficulties teachers experience in discussing mathematics. A core group of teachers and TERC staff will collaborate to develop, implement and reflect on effective models of mathematical discourse. By the end of the project, they will have: developed, implemented, and documented, promising approaches to supporting substantive mathematical discussions in elementary classrooms; analyzed the results of these approaches on teacher development and student/teacher discourse; captured classroom episodes of mathematical discourse on videotape; and developed recommendations for constructing teacher training materials.