To respond to a few points:
I suspect that driving all night allowed them to save money on hotel/motel rooms for that night. I've heard that some school trips do it that way. After Ash Lawn, they were heading to Washington, DC, where they had their first hotel reservations.
Some of the kids were wearing jackets or tee shirts for the school's sports teams (the cider-spraying idiots all seemed to be lacrosse players, judging by their logo'd clothes). Once the chaperone told me that they'd driven all the way from Lansing, MI, it was a cinch to find the school.
Some of the girls were apparently school cheerleaders. How did we know? They decided that the lawn at Monticello was the perfect place to practice their routines.
With regard to the number of chaperones, it appeared that there were two per bus, which to me seems entirely too few. The next day I looked at DH and said, "Well, it could have been worse. They could have been staying at our motel last night."
On our way home yesterday, we stopped at Montpelier, the home of James Madison. I have to say that our hearts sank when we saw a family with small children join our tour group. Two of the children were in a double stroller. The oldest was probably 8 or 9. The children could not have been more well-behaved. We made sure to compliment the parents at the end of the tour, as did the guide.