The aim of this study was to investigate the potential and limitations of peer tutoring in the development of the intonation of violin and viola students in elementary music education. Researchers have found that peer tutoring is a highly beneficial learning strategy. Peer tutoring is defined as the pairing of learners in an asymmetric relationship, who learn by teaching and start with a common, known, shared goal and an interaction framework previously structured by the teacher. After presenting a didactic proposal based on peer tutoring for the development of intonation, this research adopted a mixed-method approach to present quantitative improvements in intonation. The analysis of the pairs' interaction explains these improvements as coming from the framework fostered by the pairs and the opportunities to learn through teaching. It is concluded that peer tutoring is a very effective tool for improving the intonation of string students.