This article reports on a project based on the development of a model for outreach to support three federated mainstream primary schools in London, England to develop their understanding and practice with children with autism. The principal aim of the initiative was to ensure that knowledge and capacity within the participating schools increased; leading to better outcomes for pupils with autism. Data were collected through outreach visit observations, questionnaires completed by staff at different levels including the executive head teacher, SENCos, teachers and learning support assistants, as well as a combined SENCo report detailing individual and whole school impact -- including parent and pupil voice. The findings indicate the outreach model improved the knowledge and understanding across all levels of staffing, from senior leadership to learning support assistants which had direct impact on the provision and outcomes for pupils. This was achieved via a series of class observations by a recognised autism specialist teacher, followed by action setting sessions with class teams. After the schools were empowered and supported to monitor the outreach actions themselves, successful research-based strategies, resources and approaches were implemented more immediately leading to better outcomes for pupils and continued in-school support. This highlighted the need for in-school accountability. The findings also highlight the significant importance of the involvement of senior leadership and the subsequent impact on understanding and successful practice throughout the schools.