We use RFID in our bus-cards and stuff like that, and there you have to really try to get the blasted things registered. And you'd need those receivers all over the school to get a reliable tracking of the chips position. One in each room and corridor like.

Personally I'm not against wearing a visible ID, we adults do it all the times at work (at least in shops and healthcare) and it has never hurt me - why would it be harmful for kids? (except in new kinds of bullying)

The RFID seem to go from "We know you passed the gates to the school" to "We know you're sitting on bench 3 in corridor 2C". The first I have no trouble with (elementary school is mandatory around here) but the second just seem too stupidly expensive to be implemented in any school of size. Although the world is large, so I suppose there will always be some principals with more money than wits.