With the rise in implementation of peer-led learning in higher education, the interactions between peer instructors and their students warrant further investigation as an increasingly critical component of student learning. In this work, Teaching Interns (TIs) are undergraduate peer instructors that lead supplemental learning sessions in General Chemistry. Each week, TIs participate in pedagogy training and complete written reflections on their learning sessions. For this multicase study, six TIs were observed in their office hours over varying time periods. A qualitative approach was taken to analyze their verbal behaviors and the extent to which those behaviors matched their beliefs about teaching. Specifically, discourse analysis allowed for the characterization of the interactions between TIs and students, while analysis of TIs’ weekly written reflections provided insight into their teaching beliefs and perception of their own teaching sessions. The results presented here suggest that even at the start of the program, TIs hold some productive beliefs about teaching, though these beliefs were not always evident in their interactions with students. Over time, TIs generally shifted toward more student-centered discourse and honed their abilities to convey or elicit deeper knowledge among their students. Further, evidence from the TIs’ reflections suggest that they became better at self-monitoring their own teaching behaviors, shrinking the gap between their practices and espoused beliefs about teaching, and that they turned their focus toward student learning versus simply managing their sessions. Taken together, this work provides additional support for the further development and study of peer instruction programs.