[Fipherion]

A school system has every right to ban the sale of anything they want. As an extension the government is allowed to legislate this ban to cover all public school systems if it wanted to push the ban through the proper pipelines.

However, they shouldn't ban the food's presense on campus so if a kid's mother wants to pack their little tubby child a candy bar in his lunch, they should be allowed to.

Additionally, this sort of ban or legislation should have no effect on private schools who have the right to do whatever they want. I don't think anyone was proposing anything like this though so I guess this point is moot.