Based on a complex dynamic system approach, this study examined the dynamic of interactions between adults (a teacher and teaching assistant) and two children with ASD. We observed two preschool classrooms, each containing one child with contrasting ASD characteristics. Child engagement and adult participation during welcome time activities were observed once a month for 9 months; dramatic differences in interaction dynamics between the two classes were revealed. In the class including an autistic child with high support needs and low language ability, the active participation of adults associated with active child engagement gradually increased over the year. In the class including an autistic child with a high level of challenging behaviours (but with low support needs and typical language skills), increased variability resulted in a deep change in the landscape of attractors. Whereas the child was mostly engaged with adult participation during the first trimester, he was actively engaged without adult participation in the final trimester.