Girls on the autistic spectrum are under-represented in the research literature and it is argued that because they present differently to boys, schools are less likely to make the adjustments needed to enable them to participate fully in the inclusive classroom. This chapter presents the findings of ethnographic case studies of three girls on the autistic spectrum at mainstream primary schools and illustrates the difficulties they experience and the ways in which this is often un-recognized. The impact on them of the hidden curriculum and the implications this might have for their right to an inclusive education is considered. Data from observations and interviews 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. Lack of inclusion, particularly in terms of acceptance, had a negative impact on the girls' learning and on how they felt about school. The research also identifies a broader concept of -hidden-ness, in the attitudes and responses of the girls' teachers, peers and parents, illustrating a misunderstanding of autism in girls that contributes to a lack of support for their needs, despite their diagnosis. The study concludes that the hidden curriculum is one of a number of barriers to inclusion, resulting from the complex interaction between the girls' impairment and the environments in which they find themselves.