The purpose of the study presented in this document is to further knowledge about student teacher development contexts during field experiences. The aim is to understand the role of the mentor teacher, the classroom structure and processes, and student teacher content knowledge in the development of a mathematics teaching repertoire. This research used data gathered during the first year of a three-year study. Three student teachers were followed during their second, third, and fourth years in a four-year teacher education curriculum. Findings suggest that subject matter mentoring does not lead to better teaching. Stages of student teacher development may impinge on the ability to understand and focus on subject matter. Student teacher commitment to the learning-teaching experience as well as the relationship with the mentor remain important aspects of the practicum. Contains 22 references. (ASK)