Prior work has found benefits of interpersonal closeness, or rapport, on student learning, but has primarily investigated its impact on learning outcomes, not learning processes. Moreover, such work often analyzes the direct impact of dyadic features like rapport on learning, without considering the role played by individual factors, such as learners' prior knowledge and self-efficacy. In this paper, we investigate the intertwined impact that rapport, self-efficacy, and prior knowledge have on the process and outcomes of peer tutoring. We find that peer tutors in high-rapport dyads offer more help and prompt their tutees to explain their reasoning more than low-rapport dyads, with tutees in such dyads verbalizing their problem-solving process and proposing more steps and answers. Meanwhile, rapport is associated with increased procedural performance, but tutees' self-efficacy and prior knowledge moderate the effect of rapport on tutees' conceptual performance. [This paper was published in: "ICLS 2018 Proceedings," ISLS, 2018, pp. 600-607.]