Student teaching is a cornerstone of teacher preparation, yet it remains one of the most difficult experiences to understand. Calls for an ecological approach to research on student teaching prompted this study in which the experience is examined from the perspective of the three key triad members. Using activity theory, this study explores how their interactions in specific contexts shaped opportunities for student teachers to learn to teach language arts. The findings reveal that all members of the triad were simultaneously operating in multiple settings and facing competing demands that shaped their actions and stances. Consequently, there were numerous instances of lost opportunities for student teachers to learn to teach, including sparse feedback on teaching subject matter and few links to methods courses, plus limited opportunities to develop identities as teachers. The structures that frame student teaching and its participants have deep roots in the cultures of universities and schools that must be considered if student teaching is to maximize its potential. (Contains 4 tables.)