Trained classroom observers used the Direct Observation Form (DOF; McConaughy & Achenbach, 2009) to rate observations of 163 6- to 11-year-old children in their school classrooms. Participants were assigned to four groups based on a parent diagnostic interview and parent and teacher rating scales: Attention Deficit Hyperactivity Disorder (ADHD)-Combined type (n = 64); ADHD-Inattentive type (n = 22); clinically referred without ADHD (n = 51); and nonreferred control children (n = 26). The ADHD-Combined group scored significantly higher than the referred without ADHD group and controls on the DOF Intrusive and Oppositional syndromes, Attention Deficit Hyperactivity Problems scale, Hyperactivity-Impulsivity subscale, and Total Problems; and significantly lower on the DOF On-Task score. The ADHD-Inattentive group scored significantly higher than controls on the DOF Sluggish Cognitive Tempo and Attention Problems syndromes, Inattention subscale, and Total Problems; and significantly lower on the DOF On-Task score. Implications are discussed regarding the discriminative validity of standardized classroom observations for identifying children with ADHD and differentiating between the two ADHD subtypes.