For more than 30 years, the policy of ‘learning in regular classrooms’ (LRC) has been an approach to implementing inclusive education for children with disabilities in China. This policy has meant that many children with disabilities now attend local mainstream schools and are educated together with their typically developing peers. However, there are still many obstacles that prevent children with disabilities from being educated in mainstream schools. Further, it is hard to evaluate the experience of children with disabilities in terms of their social participation, especially for children identified as having autism spectrum disorders (ASD). This study aims to explore the social participation of primary age mainstream school children as having ASD characteristics in Beijing, China. This study adopted a multiple-case study methodological approach across 4 mainstream primary schools in two urban districts (Haidian and Fengtai) in Beijing. There were in total 6 children with ASD characteristics who were paired with a typically developing child who sat next to them. There were 6 cases conducted, including a pilot case, and 5 cases presented in this study. Multiple methods were used to explore social participation: four instruments to assess four dimensions of social participation of children having ASD characteristics; semi-structured interviews for children and teachers; and an ICF-CY-type assessment by teachers. The key findings are summarized below. Firstly, most of the case pupils were shown to have a positive or neutral social self-perception, but they seemed to have not been accepted well by their peers; the number of friendships that these case children had was less than their peers, and some of them could be considered as being isolated in the class; most of the case children were not engaged during the free time and spent time alone, while they also were unengaged and showed less interaction during the lesson. Secondly, the ICF-CY-type assessment showed the areas in which case children were experiencing difficulties and strengths in terms of activity and participation at school. It also gave a view of the environmental context which related to social participation around the case children at school. Thirdly, the analysis also showed how the academic activity was linked to social participation and was part of a wider system of social interactions. The implication of this study relates to the following points. Firstly, this study helps to identify that there is a lack of research on the social participation of children with ASD in mainstream primary schools, especially under the Chinese LRC policy. The second point is about rethinking the LRC policy from a social participation perspective so that the LRC policy could work better, especially in terms of how to balance academic and social participation. This is because there is often more emphasis on academic participation. which leads to the next point that there is also a lack of class and resource teacher collaboration and communication. Then, this study shows how to use the ICF-CY as an educational assessment for children having autistic characteristics to extend research on applying ICF from an educational perspective. Finally, what is behind the different attitudes of class and resource teachers can be seen as reflecting their views on disability. There is a need for further research to investigate class and resource teachers’ views on disability and examine what factors can influence their views and perceptions.