The current study investigated the effects of an integrative exercise intervention on the behaviours in children with autism spectrum disorder (ASD), and if they were influenced by ASD symptom severity. Sixty-six children (7.56 ± 2.03 yrs.) with ASD were enrolled and categorised as having mild (n = 22), moderate (n = 18) or severe (n = 26) symptoms of ASD by teachers using the Gilliam Autism Rating Scale 2nd edition. Participants completed a school-based, eight-week, integrative exercise intervention, consisting of three, one-hour sessions per week. Teachers rated the symptoms of ASD in each participant pre- and post-intervention using the Aberrant Behaviour Checklist. There were significant improvements in behaviours post-intervention for all children (p < 0.05; r = 0.20-0.33); however, sub-group analysis indicated that participants with severe ASD experienced greater improvements in irritability, social withdrawal, stereotypic behaviour, and inappropriate speech (p < 0.05). The findings highlight the benefits of school-based integrative exercise interventions for improving behaviours in children with ASD.