Objective: Attention deficit hyperactivity disorder (ADHD) and autism spectrum disorders (ASD) are thought to reflect the high, symptomatic extreme of quantitative trait continua. However, extreme deviations in either direction on disorder continua, high and low, may both represent maladaptive behavioral and cognitive outcomes. We aimed to test this hypothesis. Method: In a population sample of 378 children, ADHD and ASD traits were rated by parents on questionnaires that provide resolution at high and low extremes of the ADHD and ASD trait continua. ADHD and ASD traits were related to parent-ratings of internalizing and externalizing behavior problems and tests of cognitive functioning using polynomial regression. Results: The low ends of the ADHD and ASD trait continua were related to fewer behavior problems and better cognitive functioning than symptomatic ends. Conclusion: Studying the correlates of the low continuum ends may deepen our understanding of the mechanisms underlying adaptive behavioral and cognitive outcomes.