The number of pupils with autism spectrum disorders (ASD) who receive their education in mainstream schools in the UK has increased considerably over the last 10 years. Despite this increase, teachers and other support staff face a number of challenges in order to ensure that these inclusive arrangements bring maximum benefits to the children themselves, their parents and the school community as a whole. In this study we explore some of the tensions that teachers in mainstream schools may experience, many of which reflect the unique problems that the inclusion of pupils with ASD can present. In addition, we explore how these tensions may shape their views of support arrangements for those pupils. We observed 17 pupils with ASD ranging from 7 to 16 years, all of whom were placed in a regular class in one of eight mainstream schools on a full-time basis, and carried out interviews with their teachers, teaching assistants (TAs) and special educational needs coordinator. Findings suggest that tensions reported by school staff are inherently shaped by the ASD-related manifestations, particularly those pertaining to their difficulties in social and emotional understanding. These tensions determine the quality of the transactions and interactions between the teachers and the pupils with ASD. Based on these tensions, teachers form their views of the type of support that is needed for those pupils. Evidence from the data suggests that, in order for these tensions to be kept at manageable proportions, teachers rely heavily on the TA, whose role in working closely with the pupil is perceived as being indispensable. Building on the study's findings, we suggest a generic conceptualization for the successful inclusion of pupils with ASD, which is grounded in the systems theory perspective of the relationship between the teachers and these children. (Contains 1 table and 2 figures.)