Few research-developed early intervention models have been deployed to and tested in real world preschool programs. In this study, teaching staff implemented a social communication modularized intervention, JASPER, in their daily program. Sixty-six preschool children with autism in twelve classrooms (12 teachers) were randomized to receive immediate JASPER training (IT) or were waitlisted (WL) for 3 months with a 1-month follow up. Measures of core deficits (initiations of joint engagement, joint attention gestures and language, play skills) and standardized cognitive measures were improved for IT over WL children. IT teachers achieved and maintained high fidelity. Teachers can implement evidence-based interventions with significant improvements in core deficits of their children with ASD.