Bruce Schneier — the best security person working the field IMO — got wind of a small school district in Texas that's fingerprinting students when they get on and off school-buses "to prevent kidnapping." He's written a masterful deconstruction of this practice, showing why it's a stupendously dumb idea.
Let's imagine how this system might provide security in the event of a kidnapping. If a kidnapper — assume it's someone the child knows — goes onto the school bus and takes the child off at the wrong stop, the system would record that. Otherwise — if the kidnapping took place either before the child got on the bus or after the child got off — the system wouldn't record anything suspicious. Yes, it would tell investigators if the kidnapping happened before morning attendance and either before or after the school bus ride, but is that one piece of information worth this entire tracking system? I doubt it.
You could imagine a movie-plot scenario where this kind of tracking system could help the hero recover the kidnapped child, but it hardly seems useful in the general case.
