Cognitive assessments are used for a variety of research and clinical purposes in children with autism spectrum disorder (ASD). This study establishes concurrent validity of the Wechsler Intelligence Scales for Children–fourth edition (WISC-IV) and Differential Ability Scales–second edition (DAS-II) in a sample of children with ASD with a broad range of cognitive abilities. Participants achieved significantly higher overall scores on the DAS-II and nearly half the sample achieved a higher classification label on the DAS-II. The difference between overall scores is suggested to be attributable to a relative weakness in processing speed, which is assessed on the WISC-IV but not the DAS-II. Autistic symptomatology was not associated with cognitive scores, while adaptive behavior was positively associated. Neither was associated with the magnitude of difference between overall scores. Choice of assessment should be considered carefully given the systematic differences in overall scores produced in this population.