This column focuses on the valid, reliable, and useful measurement of treatment effects in children and adolescents with attention-deficit/hyperactivity disorder (ADHD) treated in practice settings. The case is presented of Polly, an 11 year-old female who was evaluated and determined to have probably met diagnostic criteria for ADHD, combined type. This column considers how to evaluate her treatment. Here, the authors discuss symptoms of ADHD, as well as sources of assessment data. They also discuss related assessment issues, such as: (1) potential bias; and (2) coordination of services. (Contains 2 figures.)