This study investigated the effects of a multiphase teacher professional development package on student use of speech-generating augmentative and alternative communication devices (SGDs). Teachers were taught (a) device operation and programming, (b) device integration and embedding using environmental arrangement strategies, and (c) systematic communication instruction using the time-delay milieu teaching procedure, within a multiple baseline design across student and teacher participants. All four teachers learned device programming and instructional procedures, and generalised as well as maintained their use. There was no effect on student SGD use during phase 1, device operation. However, all four students showed significant increases in SGD initiations during phase 2, environmental arrangement and embedding, and SGD initiations remained at high levels through phase 3, time-delay. For two students with significant disabilities, SGD initiations increased further during phase 3. All students generalized and maintained use of their SGDs for at least two months following termination of teacher professional development. This study has major implications for teacher professional development in assistive technology and augmentative and alternative communication (AAC) integration in the classroom for students with severe disabilities. Without sufficient training and support, important student outcomes such as increased participation and communication initiations for device users are unlikely to be achieved. Furthermore, this study demonstrated that measurement of student outcomes is a critical component of evidence-based professional development practices.