I think that elementary schools in Japan should stop serving lunch to their students, and I have two reasons to support my opinion.
First of all, it is dangerous. For example, some students are allergic to specific foods and they accidentally will have to get it avoided. Otherwise, they will probably get sick or even die.
Secondly, students' preferences should be respected. There are variety students such as Vegetarians, Pescatarian, and more. To solve the problem from a viewpoint of efficiently producing products corresponding to various individual needs of children, it is a smart way to bring their lunch box.
For these two reasons above, I strongly believe that schools should not deliver food to their students.