This experimental study examined ways to reduce stigma against children with attention-deficit/hyperactivity disorder (ADHD) symptoms. We randomly assigned 220 Chinese pre-service teachers to one of the four experimental groups in which they read a vignette describing a student with ADHD symptoms. The contents of the vignettes differed from one another on two dimensions: (a) the causes of the symptoms (biomedical versus social) and (b) the extent to which the student has exerted effort to improve (high effort versus low effort). Participants who received biomedical explanations of ADHD ascribed less blame to the target compared with those who received social explanations. However, the group difference was only significant in the “low-effort” group, but not in the “high-effort” group. Similarly, the “biomedical” group indicated higher levels of entity beliefs than the “social” group, but the group difference was only significant in the “low-effort” group but not in the “high-effort” group. Finally, participants in the “high-effort” condition reported a stronger intention to interact with the target compared with participants in the “low-effort” condition, whereas onset causal attributions did not affect participants’ ratings on behavioural intention. These findings may have implications for reducing ADHD stigma and bear relevance to other kinds of social stigma.