The practice of medicine involves applying abstract diagnostic classifications to individual patients. Patients present with diverse histories and symptoms, and clinicians are tasked with fitting them into generic categories. They must also persuade patients, or family members, that the diagnosis is appropriate and elicit compliance with prescribed treatments. This can be especially challenging with psychiatric disorders such as autism, for which there are no clear biomarkers. In this paper, we explicate a discursive procedure, which we term category attribution. The procedure juxtaposes a narrative about the child with a claim about members of a clinically relevant category, in this case, either children with autism or typically/normally developing children. The attribution procedure carries the implication that the child does or does not belong to that category. We show that category attributions are organised in a recurrent interactional sequence. Further, we argue that category attributions encode normative expectations about child development, such that the child is rendered typical or atypical relative to clinical and social norms. Accordingly, such categorisation devices have a moral dimension as well as a clinical one.