PurposeFood socialization is the process of influences that forms children's eating habits and preferences, affecting their well-being for life. The authors' study explores what children and adolescents eat and how they obtain food at school, aiming to describe the deleterious food socialization phenomenon. The authors focused on understanding how deleterious food socialization influences children's food well-being within the school environment.Design/methodology/approachThe authors developed a mixed methodology using structured questionnaires with open and closed questions. The authors also took pictures of the schools' canteens, which allowed deepening the understanding of the school environment. The data collection occurred in two Brazilian private schools. The schools' teachers were responsible for collecting 388 useful questionnaires from students between 10 and 14 years old.FindingsThe authors found statistically significant differences between food originating at home and school. The amount of ultra-processed foods and beverages consumed at home and taken by children and adolescents from home to school is smaller than what they buy in the school canteen or get from their colleagues. Thus, the authors suggest that the school environment tends to be more harmful to infant feeding than the domestic one.Originality/valueThis study coins the concept of deleterious food socialization: situations or environments in which the food socialization process negatively impacts one's well-being. The authors' results illustrate the deleterious food socialization phenomenon in the school environment.