Prior research on peer literacy teaching tends to be conceptualized as peer tutoring and often focuses on the cognitive aspects of reading (e.g., skills, strategies). In this multiple case study, we draw on theories of identity and positioning to propose a conceptual shift from "tutoring" to "mentoring" to also describe the affective and relational dimensions of peer literacy teaching. In our analysis, we explore how two 11th graders positioned themselves as readers and mentors in a cross-age literacy mentorship class in a public high school in the northeastern United States. Data sources include mentor interviews, field notes, and artifacts. Our multiphase coding process identified three main themes: the importance of (a) texts and (b) relationships and reciprocity to mentors' positioning, and (c) complexities of the mentor position. Findings suggest that school-based opportunities for youth to work collaboratively to understand their own and others' reading processes may contribute insights into both the affective and the cognitive aspects of peer literacy teaching.