There is a school district in the Chicago area, I think Palos Park, that has the kids wear ID's. At first I thought it was a crazy idea.
There was a news story about the whole thing and the ID's are scanned on & off the bus in addition to being worn as an all purpose card during the school day for lunch, library, etc. Not only could the parents track where the school bus was based on the tag, but it was also an easier way to make sure kids got on the "right" bus and all the kids were delivered to the "right" stop. The school district decided to do this after a kid was left on a bus--I know that the bus drivers do a walk thru; but if this helps ensure a kid is not left for hours on a bus in the Chicago winter, I think it is worth it.