Research has shown that educators may be reluctant to implement group work in their teaching due to concerns about students partaking in off-task behaviours. However, such off-task interactions have been shown to promote motivation, trust, and rapport-building. This paper details a study in which student groups were video recorded as they engaged in problem-based learning tutorials, with the aim of examining the social interaction within such settings. Eighty-five hours of data were collected from nine groups, with discursive psychology being used to analyse how group cohesion is constructed through off-topic talk such as gossiping and teasing. Two case studies are detailed in which we demonstrate how cohesion is established through a process of collective action against the ‘other’: highlighting the differences between ‘us’ and ‘them’, and how this can impact on group dynamics. There is often a discrepancy between self-reported and observed behaviour in groups and so the more we know about what actually happens in such environments, the better placed we are to support student learning. The paper concludes with recommendations on how analyses of social interaction and the management of psychological issues in problem-based learning tutorials can inform the use of problem-based learning as a teaching and learning approach.