This review evaluates the efficacy of using physical exercise interventions on improving cognitive functions in individuals with autism spectrum disorder (ASD) and/or attention deficit hyperactivity disorder (ADHD). This review includes a meta-analysis based on a random-effects model of data reported in 22 studies with 579 participants aged 3-25 year old. The results revealed an overall small to medium effect of exercise on cognition, supporting the efficacy of exercise interventions in enhancing certain aspects of cognitive performance in individuals with ASD and/or ADHD. Specifically, similar to the general population literature, the cognitive benefits of exercise are not consistent across all aspects of cognitive functions (i.e., some areas are not improved). The clinical significance of the reported effect sizes is also considered.