• We compared the effectiveness of three instruments in initially diagnosing and monitoring children with attentiondeficit disorder with and without hyperactivity (ADD/H). Twenty-one children clinically assessed as having ADD/H and meeting criteria of the Diagnostic and statistical Manual of Mental Disorders, Third Edition, were examined initially and after treatment with methylphenidate hydrochloride and placebo. The following instruments were used: the ADD-H comprehensive Teacher Rating Scale, the Connors' Parent Rating Scale-Revised, and the Gordon Diagnostic System. The ADD-H Comprehensive Teacher Rating Scale initially classified 67% of the children as having ADD/H and 14% as borderline. The Connors' Parent Rating Scale—Revised identified 71% as having ADD/H, while the Gordon Diagnostic System assessed 52% as having ADD/H and 29% as borderline. With methylphenidate treatment, the mean scores on the ADD-H Comprehensive Teacher Rating Scale displayed an increase in attention span and a decrease in hyperactivity, the Connors' Parent Rating Scale—Revised showed a significant decrease in ADD/H behavior, and the Gordon Diagnostic System mean scores indicated no significant change.