I am guessing that his speaking engagement was nearby. The school administrators probably guessed the time that the motorcade would pass by and allowed the children to watch it. I do miss Virginia schools.
JMO. It was most likely a planned pass by. He was at VMI earlier and that’s some 25 miles away from the elementary school Fairfield and off the Interstate on a side road which was a US hwy. I think the turn around was spontaneous and it was great from the children to have the opp.