Since the introduction of the Appropriate Education Act, attempts have been made to include pupils with special needs in mainstream secondary education, including pupils with autism. Statistics show that this was only partially successful. This may be partly explained by the fact that the main focus of the involved professionals (school principals, teachers) to date seems to have been mainly on the educational needs of these pupils and less on students’ sense of belonging, i.e. going to school with the feeling to be part of something, a group or community. The central question in this qualitative research is to what extent young people with autism within mainstream education experience this sense of belonging and what is needed for this. This has been investigated by means of literature research and focus groups with (former) students with autism. The first preliminary results show that students with autism indicate that they have little contact with their fellow students, which is complicated by a too busy environment (too many students, too few seats, too many stimuli). All this leads to overstimulation, fatigue, and can cause so much stress that it takes very little to completely skip school that day. In short, the most important recommendation is to create more calm and less crowded environments in schools. We conclude that social inclusion of pupils with autism in mainstream schools is essential for the success of the Appropriate Education Act but it does not come naturally: it requires active policies from schools. The project described in this article is part of a larger project in which we try to develop concrete recommendations for this purpose.