Despite the introduction of three subtypes of attention- deficit/hyperactivity disorder in DSM-IV (primarily inat- tentive, primarily hyperactive/impulsive, and combined subtypes) (American Psychiatric Association, 1994), lit- tle standardized psychometric or achievement data on individual subtypes in epidemiologically representative samples has been published. In the original DSM-IV field trials of Lahey et al. (1994), teacher ratings of academic performance were markedly lower for the primarily inat- tentive and combined subtypes but only modestly lower for the hyperactive/impulsive subtype. Similarly, for a school-based population study of the prevalence of DSM- IV subtypes in a predominantly Hispanic population, Gaub and Carlson (1997) found significantly worse teacher reports of academic problems in the primarily inattentive and combined subtypes but only modest learning prob- lems among children with the hyperactive/impulsive sub- type. Baumgaertel et al. (1995) and Wolraich et al. (1996) also found increased teacher reports of academic prob- lems for the primarily inattentive and combined subtypes compared with a no-ADHD control group and the hyper- active/impulsive subtype in two large school samples. Rohde et al. (1999), in a population sample of Brazilian adolescents, found that DSM-IV ADHD per se was asso- ciated with higher rates of grade repetition, school sus- pension, and school expulsion but no difference in estimated IQ. They did not report results by DSM-IV subtype. In addition to the DSM-IV phenomenological sub- types, other subtyping approaches have been proposed, including the presence or absence of comorbid condi- tions (reviewed by Hudziak and Todd, 1993), persistence of ADHD into young adulthood (Faraone and Biederman, Accepted January 9, 2002. From the Department of Psychiatry, Washington University School of Medicine, St. Louis. This work was supported by NIH grants MH52813 and MH31302. Correspondence to Dr. Todd, Washington University School of Medicine, Department of Psychiatry, Box 8134, 660 S. Euclid, St. Louis, MO 63110; e-mail: toddr@psychiatry.wustl.edu. 0890-8567/02/4107–08202002 by the American Academy of Child and Adolescent Psychiatry. Discrimination of DSM-IV and Latent Class Attention- Deficit/Hyperactivity Disorder Subtypes by Educational and Cognitive Performance in a Population-Based Sample of Child and Adolescent Twins RICHARD D. TODD, PH.D., M.D., NANTAWAT SITDHIRAKSA, M.D., WENDY REICH, PH.D., TED H.-C. JI, D.SC., CYNTHIA A. JOYNER, PH.D., ANDREW C. HEATH, D.PHIL., AND ROSALIND J. NEUMAN, PH.D. ABSTRACT Objective: Despite the general use of DSM-IV attention-deficit/hyperactivity disorder (ADHD) subtypes, there is contro- versy over the optimal phenotyping strategy for this disorder.This report contrasts two ADHD subtyping approaches on the prediction of cognitive function and educational achievement. Method: ADHD subtypes were determined using DSM-IV and latent class approaches for a population sample of 1,154 child and adolescent twins using parent report data.Twins completed cognitive and achievement testing and parents reported on school grades, special education placement, and history of being held back in school. Results: The DSM-IV primarily inattentive and combined subtype ADHD groups showed significant deficits in cognitive and achievement testing, worse grades, and increased use of special education resources compared with the primarily hyperactive/impulsive subtype and no-ADHD groups.Clinically relevant and less severe latent class ADHD subtypes were also associated with deficits in cognitive and achievement testing, grades, and special edu- cation use. Conclusions: DSM-IV primarily inattentive and combined subtypes of ADHD have similar significant patterns of cognitive and academic dysfunction in the general population. Latent class–defined ADHD subtypes also have patterns of serious cognitive and achievement deficits. J. Am. Acad. Child Adolesc. Psychiatry, 2002, 41(7):820–828. Key Words: attention-deficit/hyperactivity disorder, latent class analysis, school failure, learning problems. 820 J. AM. ACAD. CHILD ADOLESC. PSYCHIATRY, 41:7, JULY 2002