Both speed a child's activity. Sugar is brutal when its supply is exhausted. When the supply runs out, sugars and refined white flours dump you flat on your face. That is most probably why kids go from high to low. The normal is missing.
Most schools have junk food machines abundant.
A fast junk food store is nearby. It is the responsibility of the parents and our school administrators to remove those sources of school interruption. And interruption it most certainly is. Time after time, year after year, I have witnessed students coming into the room by way of the ceiling. By the time I got them down the wall, the bell rang and they charged out.