Background: Transgender children are known to face a wide range of barriers, difficulties and injustices at school. Few studies have focused on the educational experiences of trans pupils who socially transition at or before primary school, with no such studies in the UK. Aims: To learn about the at-school experiences of transgender children who socially transitioned at or before primary school in the UK, listening to children's and parental accounts of navigating cisnormativity in UK primary and early secondary education. Sample: The primary sample included 30 parents whose children had socially transitioned under the age of 11 in the UK. This sample was complemented with data directly from 10 of these trans children. The primary sample was accessed through six trans positive parenting groups in the UK, supplemented through snowball sampling. Methods: Semi-structured interviews produced a rich and detailed qualitative data set, that was analysed through inductive thematic analysis. Results: Three major themes are presented, highlighting experiences of (i) institutional cisnormativity in UK schools, (ii) a failure to protect trans children and (iii) evidence of educational injustice. The results demonstrate how institutional cisnormativity leaves trans pupils in unsafe educational environments, contributing to school drop-out and trauma. Conclusions: Cisnormative attitudes normalize injustice, making it acceptable for trans children to lose access to education, or to experience trauma in school. Educators, schools and school leaders need to take action to protect trans children in our schools.