In an extensive review of research on teacher preparation, Wilson, Floden, and Ferrini-Mundy (2001) pointed out that "study after study show that experienced and newly certified teachers alike see clinical experiences (including student teaching) as a powerful--sometimes the single most powerful--component of teacher preparation". They go on to suggest that cooperating teachers exert a powerful influence on the development of student teachers. However, the research evidence on the nature of this influence is both conflicting and scant. This paper reports on research that is part of a larger study aimed at understanding some of the factors that affect what prospective secondary teachers learn during the student teaching experience. The authors focus on the nature of the mathematical conversations between student teacher and their cooperating teachers.