My daughter had the diagnosis of “failure to thrive” and almost had a feeding tube. Get a note from the doctor saying your child can have whatever they want to eat or drink during the day. He should be able to eat what he wants during lunch in the lunchroom. He may need to go to the nurses office for snacks during the day, though. My daughter had to have a nurse supervise her lunch, so she ate in the nurses office. If they suggest that, I would fight that. It only alienates our kids more. Good luck!