Software engineering education is challenged by the need to convey practical experience in the context of a rich and large body of theoretical knowledge. This study investigates whether the use of open source projects can reduce the gap between theory and practice in undergraduate software engineering courses. Two qualitative case studies were conducted with students performing activities in an open source project, each one in a different course: software testing and software requirements. Results point out that the use of open source projects provides a concrete experience similar to industry experience, allows high cognitive engagement when performing tasks, favors understanding and content retention, and leads to the recognition of the usefulness of software engineering principles, techniques and methods.