Objective: Children with ADHD frequently manifest behavioral difficulties in the morning prior to school. We sought to assess the reliability and validity of the Before-School Functioning Questionnaire (BSFQ) as a measure of morning behaviors impaired by ADHD. Method: We used pre-treatment data from a randomized crossover study of 6- to 12-year-old participants comparing the methylphenidate transdermal delivery system (MTS) with a placebo transdermal system (PTS) for a total of 4 weeks. Results: The BSFQ investigator–rated scale shows very good internal homogeneity (Cronbach’s α = .91), good test–retest reliability (r = .60), good concurrent validity (r range = .42-.86), and a strong treatment effect (effect size = –.93). The self-rated BSFQ showed lower levels of reliability and validity. Conclusion: The investigator-rated BSFQ should be used in future trials of ADHD medications aimed at assessing efficacy in the morning before school.