I don't know about his school, but every month my kid's school sends a lunch menu home with the "what's happening at school this month" letter. So we do know what he's eating, and by looking at his purchases online it's pretty obvious what he likes.

But to answer the original question you do not know what he is _actually_ eating.

Whatever the lunch menu says he is eating and the actual quality of the food served could differ in the extreme.

Practically the only way you could know this is if the school posted pictures of the actual lunches being served. (Like this kid did)

I commend your school for sending menus however, better than others I have heard of.

Wow. This must have changed from when I was a kid. I never saw such a thing!