This multi-article dissertation explores the potential for the undergraduate peer mentoring experience to contribute to transformative learning for those who serve in peer mentoring or peer leadership roles. While past research has established that peer mentors experience a variety of positive outcomes associated with their leadership experience, there are gaps in the literature with regard to how the peer mentor experience can be intentionally designed as a high-impact practice for student leaders. Through three qualitative studies, as well as a comprehensive literature review, this dissertation addresses this gap by exploring what peer mentors report learning through their mentoring experiences (Article #1), the types of experiences that contribute to transformative learning (Articles #2 and #3), and how transformative learning can be facilitated through a particular designed training intervention (Article #4). Based on the findings of these four studies, an emerging framework is proposed to describe the characteristics of high-impact and transformative PM learning environments. This framework suggests that transformative PM learning is most likely when (a) the learning of PMs themselves is an explicit objective of the program or initiative, (b) PMs are engaged in purposeful routines and structured practices that facilitate learning, (c) PMs are exposed to unfamiliar and challenging situations in their mentoring practice, (d) theoretical and conceptual understandings (e.g., selected readings) are integrated into PM development; (e) PMs are provided with frequent and structured opportunities for reflection on their experiences, and (f) PMs are part of a supportive mentoring community. Recommendations for the design of high-quality PM learning environments are made based on the elements of this framework. Additionally, directions for future research on peer mentoring as a high-impact practice are made.