In comparison to healthy children, cases with Attention Deficit Hyperactivity Disorder (ADHD) score lower at subtests of Wechsler Intelligence Scale for Children-Revised (WISC-R). According to the research hypothesis, the lower scores in subtests of WISC-R originate from disordered attentional processes. Sample (age range: 72-149 months) included 143 healthy boys and 215 boys in the ADHD group (Predominantly Attention Deficit: n = 72, Predominantly Hyperactivity/Impulsivity: n = 41, Combined: n = 102). Participation was conditional to informed consent of the parents and approval of the participants/cases. Cases with comorbidity and medication were not included in the DEHB group. Intelligence was measured using WISC-R, types of attention were measured using Stroop Test TBAG version, Cancellation Test and Visual Aural Digit Span Test-B Form. In line with the types of attention that they represent, neuropsychological test scores loaded on three different factors. Except the digit span score, WISC-R scores loaded on a fourth factor. Scores of the DEHB group was significantly lower than that of the healthy control group in 9 out of 12 WISC-R scores. When types of attention were statistically controlled, 7 of the previously significantly different scores ceased to exist. These findings show that the lower scores of the DEBB group in subtests of WISC-R should not be explained by deficits in the cognitive processes that the subtests specifically intend to measure. These findings support the hypothesis that the lower scores are due to a basic inability to attend and are thus secondary to this disorder.