As introductory college science courses transition from large, passive lectures to more student-centered active learning environments, additional instructional support may be needed. Peer Learning Assistants (PLAs) can aid course transformations by helping facilitate active learning and peer engagement among students in the classroom. Pedagogical training prepares PLAs to guide student learning through a variety of evidence-based strategies. However, little is known about how PLAs enact these pedagogical strategies to promote learning during student interactions. In this qualitative study, we sought to understand the ways in which PLAs support student learning in introductory college biology courses. Thematic analysis of interviews with PLAs revealed they use both relational and cognitive strategies while interacting with students. Relational strategies included making students comfortable and attending to student differences to create an inclusive learning environment. Cognitive strategies related to building students' understanding by asking guiding questions, eliciting student thinking, and providing alternative explanations. By engaging in these actions with PLAs, students may learn to adopt similar practices. Therefore, PLAs facilitate student-centered instruction by guiding student thinking and fostering student development of learning strategies.