A mathematics methods course is a critical site for intervening on prospective teachers' past experiences with mathematics, which have often left them without a meaningful understanding of mathematical content, appreciation of what mathematics entails, or confidence in their own ability to do and to learn mathematics. This paper examines the role of a preservice mathematics methods course in helping beginning elementary teacher candidates re-examine and move beyond these past experiences in order to help them learn to teach mathematics for understanding. The paper combines a conceptual analysis of the role of past experiences in learning to teach mathematics with a description of new experiences that were specifically designed to intervene on the past experiences. The new experiences lead the student teachers to reconstruct their prior experiences and to redirect the course of their future with the subject, in this case, mathematics. The conceptual analysis is elaborated with discussion of the prospective teachers' reactions. (Author/JD)