Adaptive behavior is a critical metric for measuring outcomes in those with autism spectrum disorder (ASD). Executive function skills predict adaptive behavior in youth with ASD with average or higher IQ; however, no study has examined this relationship in ASD with lower IQ (IQ ≤ 75). The current study evaluated whether executive function predicted adaptive behavior in school-age youth with ASD with lower IQ, above and beyond nonverbal IQ. We examined adaptive behavior and executive function through informant report on 100 youth with ASD with lower IQ. Executive function skills explained variance in adaptive social and communication domains, beyond nonverbal IQ; monitoring skills played a significant role. This research suggests that malleable skills like executive function may contribute to functional outcomes in this population.