We analyzed the results of high school teachers' ratings of symptoms of attention deficit hyperactivity disorder (ADHD) and oppositional defiant disorder, as well as school-related impairment of 875 adolescents. One hundred forty-three teachers at 19 high schools across 4 states each rated 6 students from their first-period classes according to selection criteria that led to ratings for 3 male and 3 female students. Factor analyses were conducted on the symptom measure to test hypotheses pertaining to the divergence of impulsivity and hyperactivity dimensions. Normative values for the Disruptive Behavior Disorder-Teacher Rating Scale and Impairment Rating Scale are reported, as well as important differences related to age, race, and gender. Gender and age contrasts revealed that boys were rated as more symptomatic and impaired than girls and younger adolescents were rated as having more problems than older adolescents in most areas. African American adolescents were rated higher on measures of symptoms and impairment than their Caucasian peers. Large differences in normative levels of hyperactivity/impulsivity and inattention are reported that are consistent with a reduced likelihood of a diagnosis of ADHD-C as children get older. Implications for the interpretation of ratings from high school teachers are discussed.