The aim of this study was to examine the relationships between intelligence, ratings of behavior, and continuous performance test scores for a sample of 117 children aged 6–16 years who were referred to a specialty clinic. The sample was comprised of children who had a primary (45%) or secondary (36%) diagnosis of ADHD. All children were given the Wechsler Intelligence Scale for Children Third Edition (WISC-III), Cognitive Assessment System (CAS), Conners' Continuous Performance Test (CPT), and Conners' Parent and Teacher Rating Scales—Revised, Long Form. Correlations between Conners' Behavior Rating Scale and Conners' Continuous Performance Test were uniformly low and non-significant (the highest correlation was .17). Correlations between the WISC-III and Conners' Parent Rating Scale were all non-significant, but Teacher Ratings showed significant correlations between most of the WISC-III factors and the Cognitive Problems/Inattention scores. Few significant correlations were found between CPT with the WISC-III and CAS. These results suggest that practitioners should expect to find a lack of consistency between the scores provided by these measures and should be conservative of their use in clinical settings.