A study in an Australian university investigated 150 pre-service teachers' responses to and participation in discourses of attention deficit hyperactivity disorder (ADHD). Interesting data surfaced around the notion of "labelling" children with ADHD. It seemed that the pre-service teachers did not believe "ADHD" to be a label. Whilst the literature reviewed acknowledged diagnosing a child with ADHD to be tantamount to labelling (that is, "ADHD" is a medical diagnostic label), the pre-service teachers in this study differentiated diagnosis from labelling and cast labelling as occurring "in the classroom" sometime "pre-" or "post-" diagnosis. Speaking of diagnosis and labelling in this way re-defines an object of dominant labelling discourse: "doctor as labeller" is replaced with notions of "teacher as labeller". Using Foucault's "rules of discursive formations" to frame its analysis, this study pondered the pre-service teachers' conceptions of labelling and in doing so revealed a "teacher as labeller" discursive formation. This article provides examples of how this discursive formation features in pre-service teachers' talk and outlines an important implication of the "teacher as labeller" discursive formation, namely that it enables teachers to cement their role in the ADHD medical diagnostic apparatus. (Contains 6 notes.)