In this single case study, we explore how four preservice math teachers developed their self-efficacy through a peer tutoring experience in a college math lab. Using pre- post self-efficacy assessments, faculty observations, researcher observations, faculty interviews, and interviews with the preservice teachers themselves, our analysis describes how reflection alongside vicarious experience, mastery experience, social persuasion, and psychological arousal supported self-efficacy development in the preservice teachers. We find that within the self-efficacy framework, social persuasion and psychological arousal were embedded in direct experience, and that different types of experiences spurred the preservice teachers to reflect on different aspects of their role. Our study suggests opportunities to cultivate teacher self-efficacy, self-awareness, and reflection through early field experiences.