We examined whether instructional materials describing how to rate child ADHD symptoms would improve the accuracy of mothers' ratings of ADHD symptoms presented in standard child behavior stimuli, and whether instructions would be equally effective across a range of maternal depressive symptoms and family incomes. A community sample of 100 mothers with 5 to 12 year old sons were randomly assigned to either receive or not receive the instructions. All mothers watched standard video recordings of boys displaying nonproblem behavior, ADHD symptoms, ADHD plus oppositional behaviors, or ADHD plus anxious behaviors, and then rated the ADHD symptoms of the boys in the videos. These ratings were compared to ratings of the boys' ADHD symptoms made by objective coders. Results indicated an interaction such that the instructional materials improved the agreement between mothers' and coders' ratings, but only for mothers at lower family income levels. The instructional materials improved all mothers' open-ended responses regarding knowledge of ADHD. All mothers rated more ADHD symptoms in boys with comorbid oppositional or anxious behaviors, and this effect was not reduced by the instructional materials. The potential utility of these instructions to improve the accuracy of ratings of child ADHD symptoms is explored.