Although much has been written about the agreement of parents and teachers regarding the diagnosis of attention-deficit/hyperactivity disorder (ADHD), some uncertainty remains about their agreement when assessing change during drug treatment. To address this issue, we analyzed data from a placebo-controlled short-term study and an open-label long-term study of ADHD children treated with OROS methylphenidate (MPH). Both reporters agreed that OROS MPH was efficacious for symptoms of inattention/overactivity and oppositionality/defiance and that the effect was greater for inattention/overactivity than oppositionality/defiance. Thus, in clinical trials, having two reports may not be absolutely essential for assessing the efficacy of ADHD medications. We also computed diagnostic efficiency statistics and found a high probability that parents would confirm teacher reports of therapeutic improvement and a somewhat lower probability that teachers would confirm parent reports of therapeutic improvement. In contrast, neither reporter was likely to confirm the other reporter's report of no improvement or worsening. Thus, when given a report of no improvement from one setting, clinicians cannot be certain about clinical status in the other setting. For symptoms of oppositionality and defiance, we also saw that parent- teacher agreement about improvement was better than agreement about lack of improvement. However, for these symptoms, teacher reports were somewhat better predictors of parent reports than vice-versa.