This paper examines a preservice teacher initiative whose overarching goal is to begin to reverse the cycle of educational failure for students labeled "at-risk." Although research in teacher preparation has explored the ways in which preservice teachers learn to teach, few studies have focused on how teaching in an alternative high school interacts with and complicates the process of learning to teach mathematics. The study discussed in this paper investigates the influences of a mathematics teaching experience in an alternative high school on five preservice teachers who planned, designed, and taught an integrated mathematics class for at-risk students who were enrolled in the school. The findings reveal that the teaching experience provided the preservice teachers with a vehicle for reflecting on and reconsidering their conceptions of mathematics teaching and perceptions of at-risk students. The analysis suggests that the experience enhanced the preservice teachers' perceptions of at-risk students, prompted them to set higher expectations for the students, and encouraged them to engage in conceptually-focused mathematics teaching. In addition, teaching in the alternative high school provided the preservice teachers with experiences that fostered an understanding of how at-risk students think mathematically and how to cultivate mathematical thinking in at-risk students.