From e-Gov Laws.
The School Lunch Act says that school lunch helps children grow healthy in body and mind, and plays an important part in building a correct understanding of food and good judgment about it.
Article 2 lists seven goals: (1) keep and improve health through good nutrition; (2) understand everyday meals, build the judgment to eat healthily, and form good eating habits; (3) make school life richer and build a cheerful, cooperative spirit;
(4) understand that our food depends on the gifts of nature, and respect life and nature; (5) understand that many people’s work supports our food, and value work; (6) understand the fine traditional food cultures of Japan and its regions; (7) understand how food is produced, delivered and used.
The law’s school lunch is the lunch served to pupils at compulsory-education schools: elementary schools, junior high schools and similar schools.
There is no single right answer. Talking it over with someone at home is a good way to learn.