I knew too many students in my high school who subsisted on soda and chips, but the school lunches there weren't much better. I was among the lucky tier who often got to eat healthful lunches lovingly made by a parent.
But I also recall once hitting another student with my lunch bag, and unexpectedly hurting him, because the bag contained a soda.
I guess it all depends on the quality of the school's food. . . not that I have ever encountered a decent public school lunch.