This study reports on the effects on first year pre-service teachers' epistemological beliefs, and teacher practices, of participation in a social constructivist-focused mathematics program. Aligned with social constructivist tenets the researcher-teacher asserts that crucial in the development of a teacher's epistemological position is the opportunity for pre-service teachers to explore and develop mathematics and learning as socially constructed. The study's major aims were to contribute to knowledge about pre-service teachers' mathematical understandings and understandings of how an individual's epistemology influences both the teaching and the learning of mathematics, and to ascertain the implications of building mathematical experiences for learners that are framed by social constructivist understandings.