At the approximate 10 minute mark, Keith picks up a book dropped by an Extra (student), who is then seen walking into the School in the background of the continuing shot. Less than 20 seconds later, the same Extra is seen walking in the near background of the next shot - which looks back out towards the front lawn of the School.
When Laurie and Lester arrive at the parking area, it's obvious that the city below them is a photograph.
In the school gym locker room, the clock on the wall has the time at 10:10, the universal time that is set on virtually every clock you buy. Evidently, the clock was purchased for the scene, and not set to a more appropriate time.