Purpose This paper describes the research that underpins the development of EATS (the Environmental Assessment Tool for School meals), a life cycle-based decision support tool for local authorities and their contractors responsible for providing catering services to schools. The purpose of this tool is to quantify the carbon footprint (CF) and water footprint (WF) of the meals served in order to identify hotspot meals and ingredients, and suggest simple, yet transformative, reduction measures. A case study is used to test the tool, comparing the impacts of 34 school meal recipes. Methods The tool utilises secondary data to calculate values of CF and WF for a school meal from cradle to plate. This includes three phases: (1) food production, (2) transport of each ingredient to a generic school kitchen in the UK, and (3) meal preparation. Considerations for waste along the supply chain are included. After testing the tool against a set of nutritionally compliant meals, a sensitivity analysis was performed to investigate the influence of the origin and seasonality of the ingredients, transport mode and cooking appliances used on the final results. Results and discussion The results of the case study show the predominance of the production phase in the overall carbon footprint and that there is a strong tendency towards lower impacts for meat-free meals; however, this is not always the case, for instance some of the chicken-based meals present lower impacts than vegetarian meals rich in dairy ingredients. The sensitivity analysis performed on one of the meals shows that the highest value of CF is obtained when the horticultural products are out of season and produced in heated greenhouses, whilst the highest value of WF is obtained when the origin of the ingredients is unknown and the global average values of WF are used in the analysis; this defines a crucial data need if accurate analyses are to be uniformly possible. Conclusions This article focuses on the potential offered by the public food sector for a transformative reduction in the environmental impact of urban food consumption. The results presented prove that careful menu planning and procurement choices can considerably reduce the overall environmental impact of the service provided without compromising quality or variety. This research thus supports those responsible for making these decisions via a user-friendly tool based on robust scientific evidence.