Wechsler intelligence scale for children-third and -fourth edition predictors of academic achievement in children with attention-deficit/hyperactivity disorder

IQ and achievement scores were analyzed for 678 children with attention-deficit/ hyperactivity disorder (ADHD; 6-16 years of age, IQ >= 80) administered the Wechsler Intelligence Scale for Children-Third Edition (WISC-III, n = 586) and Wechsler Intelligence Scale for Children-Fourth Edition (WISC-IV, n = 92). Approximately 76% of children in both samples were identified with a leaming disability (LD). LD in written expression was more common than in reading or math. For both the WISC-III and the WISC-IV, full-scale IQ was the strongest single predictor of achievement in all areas. The verbal subtests comprising the Freedom fiom Distractibility/Working Memory Index (FDI/WMI) and Verbal Comprehension Index were more highly correlated with achievement scores than the nonverbal subtests on both the WISC-III and WISC-IV. The most powerful predictors of LD, however, were the FDI/WMI and Processing Speed Index (PSI) subtests. These findings suggest that verbal intelligence is more influential in determining level of academic achievement, whereas cognitive abilities assessed by FDI/WMI and PSI are more important in determining LD in children with ADHD.