The transition into formal schooling environments is a difficult period of change for many children. For some children with autism spectrum disorder, hereon referred to as autism, delays in their development of school readiness skills (e.g., following directions, attending to tasks) may exacerbate these difficulties. With a large proportion of children with autism educated in mainstream settings, it is critical that teachers in these settings are well equipped to support their transitions. For many children, this includes continuing to support their development of these school readiness skills, into the first year of formal schooling. Reviews of the autism treatment literature have resulted in the identification of empirically supported treatments (ESTs), a number of which specifically target school readiness skills. Whereas previous researchers have examined the extent to which ESTs are used by early intervention providers and special education teachers, this project was designed to investigate knowledge and use of those ESTs targeting school readiness skills in a population of general education teachers. It was also important to understand the factors that influence teachers’ support for students, to develop a process for supporting general education teachers as students with autism enter school. The research presented here involved a mixed-methods design over three phases. In Phase One, a survey was used to investigate general education foundation year teachers’ knowledge, use, and perceptions of social validity of these ESTs. Phase One established that general education teachers were currently using a combination of ESTs and non-ESTs in their support of students with autism and revealed that teachers perceived many of these ESTs to have a high degree of social validity. In Phase Two, qualitative interviews with teachers identified barriers and facilitators to their use of ESTs and support for students with autism more broadly. These interviews highlighted that teachers’ capacity to provide support to students was impacted by several factors, including their experience, and competing demands of the classroom. The analysis also identified that provision of training, adequate within school supports, and increased collaboration during transitions could assist in mitigating some of the challenges faced. Finally, in Phase Three, a qualitative approach was employed to determine the social validity of a proposed online tool harnessing three key factors likely to be influential during transitions and involved interviews with stakeholders in the transition to school. Stakeholders interviewed reported that the online tool proposed could provide value to users and was an acceptable and appropriate means of accessing information and other professionals. Taken together, these studies provide a unique insight into current capacity, challenges and opportunities for optimising outcomes for students with autism, and a potential avenue to achieve positive change within and across mainstream settings.