U.S. school teachers are routinely on duty during lunch periods, as crowd control, so I'm not sure that's really a difference.
U.S. school lunches are absolutely woeful. Just check out the #thanksmichelleobama pictures on twitter for a general overview[1]. I think there's got to be some big kick-backs given by the packaged food distributors, because there is no way that frozen pizza and McRib sandwiches are cheaper than cooking actual food.