IBI is costly and there are currently long waitlists of children who are in need of treatment. The investigators have clinical and ethical obligations to determine more appropriate alternatives to IBI for children making few gains because all children with autism deserve treatment based on their needs. This study is designed to determine the effectiveness of a functional skills group intervention, based on the principles of applied behaviour analysis, for children responding slowly to IBI. Specifically, it will investigate the effectiveness of functional behavioural skills training in addition to IBI at increasing a child's independence in day to day communication and self-help skills and reducing behaviour problems, as well as increasing parental competence and decreasing caregiver strain compared with IBI alone. Having an effective alternative to IBI for children making few gains is relevant from the standpoint of i) preventing exposure to potentially intrusive interventions for those children making few gains in IBI, ii) allowing children making few gains in IBI to access effective treatment, iii) opening limited IBI spots for children who would benefit from IBI, and iv) making better use of limited health resources. Overall, the results will be of interest to parent, clinicians, researchers and funding bodies.