This study examined the latent structure and validity of inattention, hyperactivity-impulsivity, and sluggish cognitive tempo (SCT) symptomatology. We evaluated mother and teacher ratings of ADHD and SCT symptoms in 140 Puerto Rican children (55.7% males), ages 6 to 11 years, via factor and regression analyses. A three-factor model (inattention, hyperactivity-impulsivity, and SCT) provided the best fit for both sets of ratings. Inattention was the strongest correlate of lower scores on neuropsychological, achievement, and psychosocial measures. Externalizing problems were most strongly associated with hyperactivity-impulsivity, and internalizing problems were most strongly associated with parent-rated SCT and teacher-rated Inattention. SCT was not associated with executive function but was negatively associated with math. Inattention accounted for a disproportionate amount of ADHD-related impairment, which may explain the restricted discriminant validity of DSM-IV types. The distinct factors of hyperactivity-impulsivity and SCT had unique associations with impairing comorbidities and are roughly equivalent in predicting external correlates of ADHD-related impairment.