That's not a sole US thing. We have schools of hundreds to in the thousand here as well. Then again they build new buildings if the school grows too big (usually, not always).
Usually the kids used go home for lunch and it was an hour (easily done if you live withing 15min walking from the school). These days you also have schools with shorter lunches and shorter schooldays probably due to more parents both working (kids stay at school then). Lunches are staggered in that case, to not have everyone inside/outside all at once.
That's not a sole US thing. We have schools of hundreds to in the thousand here as well. Then again they build new buildings if the school grows too big (usually, not always).
Usually the kids used go home for lunch and it was an hour (easily done if you live withing 15min walking from the school). These days you also have schools with shorter lunches and shorter schooldays probably due to more parents both working (kids stay at school then). Lunches are staggered in that case, to not have everyone inside/outside all at once.