There is evidence that feeling a sense of belonging supports pupils’ social acceptance and is a protective factor against harmful psychological outcomes. Despite this, limited research has considered autistic girls’ belonging experiences in mainstream schools and what needs to change to facilitate belonging. Personal constructs and lived experiences of school belonging were explored using semi-structured interviews and personalised activities (e.g. drawings and poetry) with 18 autistic adolescents assigned female at birth (AFAB) in mainstream school settings. Participants were involved in the data analysis process as they commented on codes and themes. We generated three main themes from the data. Theme 1) “Wanting to feel seen and heard” focussed on the recognition and validation of the autistic experience and identity, and how understanding of autism informs practice. Theme 2) “Longing to belong” focussed on the young people’s experience of trying to develop relationships with others, their experiences of trying to fit in, and the impact that this had on them. Theme 3) “Sensory build-up results in shutdown” focussed on the overwhelming nature of the sensory environment in school, and the impact that this has on both the learning and social experience. All participants want to be externally valued, heard, and involved in the school community. However, aspects of masking, stigma and sensory experiences limit the girls’ belonging in school. Implications for professionals and future research are discussed along with recommendations. The latter can inform future school mental health policy and practice to create emotionally healthy school environments, in which autistic young people can be their authentic selves and have their best lives.