The number of children diagnosed with autism both nationally and internationally is increasing dramatically. Development of social-communication abilities is a major difficulty for those on the Autism Spectrum (AS). Research highlights the positive impact of supporting parents to adopt facilitative communication strategies when interacting with their children on the AS. However, there is a paucity of research exploring the impact of enhancing knowledge and use of such strategies in schools. In response to this, a social constructivist model of professional development (PD) was developed and evaluated using a multiple case study of five different autism-specific classrooms in the Republic of Ireland. Findings indicate that the interactions within the classrooms changed, the adults' communication became mainly facilitative, the duration of positive shared engagement increased significantly, and the pupils' rate of communication increased, particularly their initiations. The More Knowledgeable Other (the first author) played a pivotal role in supporting the adults' active engagement in the learning through facilitation and incorporation of learning activities. This article argues for a model of PD in which the participants are actively engaged in learning activities that require them to implement the content, and to reflect and problem solve both individually and within a group.