Absusers of this system would be easily weeded out (Score 1)

If the same group of people were to be coming to at exactly the same time often, it would become obvious to a log analysis type program. On that topic I also wonder if a RFID card reader can recognise that many cards at once.. As the readers don't have a massive range, they would most probably place two of them at each side of the entrance doors to a class, not allowing the cards that were left unread to be recognised.