This article presents the findings of ethnographic case studies of three girls on the autistic spectrum attending mainstream primary schools and illustrates the difficulties they experience and the ways in which these are often unrecognised. The observations of the girls and subsequent individual interviews with their mothers, class teachers, SENCO's and ultimately themselves, reveal the personal adjustments the girls make in response to the hidden curriculum and the ways in which these go unnoticed, effectively masking their need for support, and contributing to their underachievement in school. The research also identifies a misunderstanding of autism in girls by some teachers that contributes to a lack of support for their needs, despite their diagnosis. Teachers need to understand how autistic girls present, and how they learn, if they are to recognise the need to illuminate the hidden curriculum. The implications of these findings are that without this awareness autistic girls in mainstream settings are also at risk of limited access to the known curriculum and of social isolation.