In design education, challenge-based approaches where students work on real industry problems are becoming increasingly common. Such education relies heavily on teamwork. Consequently, this requires educators to form teams that can deliver the desired outcome while fomenting learning and collaboration among teammates.Most of the literature on team formation in design education is focused on larger cohorts, of dozens or hundreds of students, where slackers or free riders are a major concern. In the present study, we focus on team formation within smaller cohorts, of pre-selected, highly motivated students. We use two global networks of collaborating universities teaching design thinking. In each project, a multidisciplinary group of three to five students from one university is teamed up with a similar group of students from a second university along with a corporate sponsor that provides the challenge. We selected teaching team members from participant universities to interview about their practices regarding team formation. Both the interviewees themselves and their institutions had multi-year experience in forming multiple teams out of a group of pre-selected students. We interviewed 6 teaching team members (from 5 universities) for about an hour each. The interviews were recorded, transcribed, and analysed, to contrast their practices to each other as well as to theory. Practices range from a halfday session to a multi-week warm-up period prior to the proper course. Our findings are that current practices have evolved through trial and error over time and are only partially grounded in theory on team formation.