Context: It is common practice in academia to have students work with “toy” projects in software engineering courses. One way to make such courses more realistic and reduce the gap between academic courses and industry needs is getting students involved in Open Source Projects with faculty supervision. Objective: This study aims to summarize existing information on how open source projects have been used to facilitate students' learning of software engineering. Method: A systematic mapping study was undertaken by identifying, filtering and classifying primary studies using a predefined strategy. Results: 53 papers were selected and classified. The main results were: a) most studies focus on comprehensive software engineering courses, although some papers deal with specific areas; b) the most prevalent approach was the traditional project method; c) surveys are the main learning assessment instrument, especially for student self-assessment; d) conferences are the typical publication venue; and e) more than half of the studies were published in the last five years. Conclusions: The resulting map gives an overview of the existing initiatives in this context and shows gaps where further research can be pursued.