The New York Times > Technology > In Texas, 28,000 Students Test an Electronic Eye:

"In the long run, however, the biggest problem may be human error. Parents, teachers and administrators said their primary worry is getting students to remember their cards, given they often forget such basics as backpacks, lunch money and gym shoes. And then there might be mischief: students could trade their cards."

Sounds like a pitch to implant ID chips in the kids... I don't think we're ready for that yet. I hope not.