Gender construction through clothing for children in French schools is particularly observed until the 1970s. Whether through strict regulations or simply by monitoring dress codes in a gendered school, the clothing differentiation between girls and boys takes place in the sharing of a common role: that of the schoolchild. The opening of schools to the notion of co-education through the cohabitation of girls and boys in the same spaces, leads to the attenuation of this distinction in gendered dress codes. The political and pedagogical choices which contribute to the mixing of genders in school, and to certain extent the estate constraints of the school institution after the Second World War, have certainly contributed to the appearance of a mixed fashion inspired by male style and reinvents the codes of children's fashion. The girls' pants are representative of this emancipation of childrenswear which, from the schoolyard, will influence adults dress code. Based on the analysis of regulatory texts, photographs of schoolchildren and fashion archives, this chapter first explores gendered fashion in French schools of the 20th and 21st centuries and the echo of this movement in school regulations. Secondly, the study of the shapes and types of clothes worn by pupils, and more specifically the appearance of trousers among girls, sheds light on the influence of the institution on gender construction in childhood, and finally on the fashion industry in a particular historical context.