This paper's purpose is to present the findings of exploratory research performed at TU/e innovation Space to gain a better understanding of what students learn in extracurricular student teams. Having a better understanding of student learning can help us make such learning more visible, which has a positive impact on students' development of professional identity and employability. The scope of this study includes interviews with five alumni from student teams and an analysis of its outcomes. The results of the interviews' analysis showed that students recognized that they experienced learning gains because of their participation in student teams. However, the process of describing the learning gains in a detailed way is not easy for them, showing that their extracurricular efforts did not make these learning gains explicit. Students reported learning gains associated with personal and professional skills (CDIO syllabus section 2) and interpersonal skills, collaboration, teamwork, and communication (CDIO syllabus section 3). Peer interactions and learning by doing were the most relevant media that promoted those learning gains. Finally, we conclude that additional methods such as observations during teamwork can help understand the mechanisms that facilitate learning.