The aim of this ethnographic field study was to investigate the influence of school-day social interactions on the well-being and social inclusion of children diagnosed with ADHD. The empirical data consisted of participant observations and informal interviews over a three-month period at a Danish primary school. Two ADHD-diagnosed 11-year-old boys in the fourth and fifth grades were followed on an alternating basis. The field notes were analysed using a qualitative content analysis that incorporated Etienne Wenger's concepts of social identity and participation. The results revealed that the effects of school-day social interactions are complex and situation dependent. Medication, friendships and relationships with teachers and other adults strongly influence how children diagnosed with ADHD participate in social interactions and, consequently, how they thrive. We argue that it is important to emphasise the mediation of these children's participation in the classroom community throughout an entire school day to ensure their social inclusion and well-being.