Current eating patterns are damaging the environment and there is a need for dietary guidelines to address this issue. Schools can act as springboards to promote sustainable food habits. However, unlike other European national dietary guidelines, the Spanish school dietary guidelines do not include environmental sustainability guidance. In this study, a life cycle assessment (LCA) approach was used to quantify the carbon footprint (CF) of school menus designed following the Spanish school dietary guidelines and adjusting to approximately 610 kcal/lunch-meal. To do so, the menus assessed were the baseline menu and six alternative menus served in schools (the menu without dairy and without legumes, the menu without meat, the menu without fish, the menu without eggs, the hypocaloric menu and the astringent menu designed to address intestinal illnesses). The CF of the baseline menu was 24.39 kg CO2 eq/person/monthly lunch-meal which resembled, to some extent, the CF of the Mediterranean diet obtained for adults and approximately 700 kcal/lunch-meal. Regarding the alternative menus, the astringent menu and the menu without meat presented the lowest CF, being 14.77 kg CO2 eq/person/month and 17.11 kg CO2 eq/person/month, respectively. It is recommended that Spanish dietary guidelines include the environmental performance of foods to optimize school menus and favor a gradual transition towards a more environmentally-friendly diet.