We studied the association between an adult’s behavior and episodes of social engagement (ESEs) in young children with autism during play-based assessment. ESEs were defined as events in which a child looked toward the adult’s face and simultaneously showed an additional form of communicative behavior. The adult’s behavior before each ESE, and before time-sampled control periods, was rated using Coding Active Sociability in Preschoolers with Autism (CASPA). As predicted, adult musical/motoric activity, communications that followed the child’s focus of attention, scaffolding through social routines, imitations of the child, and adult repetitions were significantly more prevalent before ESEs, but cognitive assessment activities, adult inactivity, and “ignoring” were significantly less prevalent. We consider the implications for understanding the developmental psychopathology of autism.