The current study examined the incremental utility of rating scales, a structured diagnostic interview, and multiple informants in a comprehensive assessment of attention-deficit/hyperactivity disorder (ADHD). The sample included 185 children with ADHD (M_age = 9.22, SD = 0.95) and 82 children without ADHD (M_age = 9.24, SD = 0.88). Logistic regressions were used to examine the incremental contribution of each method within an assessment of ADHD. Results indicated that information collected from a structured diagnostic interview was unable to significantly improve a prediction model including parent and teacher ratings (Block ² = 0.91, = .64). Teacher ratings on symptom-based scales resulted in significant model improvement beyond parent ratings alone (Block ² = 48.47, < .001). Exploratory analyses indicated that using behavioral rating scales correctly classified all participants by diagnosis. Clinical implications are highlighted, and future research directions are discussed.