A simulator driving test (SDT) and two neuropsychological tests, the Useful Field of View (UFOV) test and the Test of Variables of Attention (TOVA) were evaluated with regard to validity for fitness to drive on 51 young clients diagnosed with attention deficit hyperactivity disorder (ADHD), 33 of whom also had autism spectrum disorder (ASD), and 38 adolescents without a neurodevelopmental diagnosis. The results show generally much greater variability and significantly poorer performance in the SDT and the TOVA for clients with ADHD/ASD compared with the control group. The SDT results were strongly intratest correlated, but had no interest correlation with either the UFOV test or the TOVA. The greater variability among clients with ADHD/ASD suggests greater effort and susceptibility to motivational issues and decline in sustained attention over several tests. In conclusion, the SDT is sensitive and has good face validity, and the TOVA is sensitive to neuropsychological aspects of safe driving. The SDT and the TOVA thus complement each other, and discrepancy between test scores calls for special consideration.