The aim of this study was to perform a nutritional assessment of the menus served in school canteens and to verify their effects on the nutrition of schoolchildren. We selected three collective catering companies that offered ~53 500 menus/d in 369 schools in Spain's Mediterranean area (Valencian Community). The study included four public schools with different management models as well as different supply patterns. Considering the weight of the servings, the caloric contribution of the menus was estimated. Great diversity was seen both in the same school throughout the week and between the four schools (School 1: 298-946 kcal; School 2: 465-1185 kcal; School 3: 395-656 kcal; and School 4: 374-966 kcal). The energy intake from carbohydrates complied with the recommendations in three of the four schools, the energy provided from proteins was adequate in all of the schools, and the energy from lipids was higher than the recommended values in Schools 1 and 2, lower in School 3, and compliant in School 4. The most abundant fatty acids in the menus were oleic, linoleic, and palmitic acids. The sodium content in the rated menus was 229 ± 72 mg/100 g. The highest salt content came from menus that included a precooked dish, processed meat, or both. It is necessary to review school menus and adjust the size of the servings to the age of the children. Correct nutritional education is essential for both kitchen staff and school canteen monitors.