XP is a lightweight process that provides principles for guiding projects and relies on the participants for its success. However, despite these guidelines, projects can be unsuccessful. We have previously identified that participants? levels of "buy-in" into the ethos of the methodology is a significant determinant of project success. This paper investigates how team formation influences buy-in and how buy-in, in turn, effects success, learning and working attitude within an academic environment. The empirical study shows that teams comprised of people with similar understandings of, and attitudes towards, the process tend to have a higher level of buy-in and, as a result, exceed their expected performance potential.