I was thinking more along the lines of the teachers fitting their own cameras. I have a very good two inch camera which will connect to a dvd/vhs recorder. It can be concealed easily and can operate wirelessly. A teacher could place one in the music room shortly before a lesson. The recording would be kept by the teacher and would only need to be produced if required as evidence. So, this would not be Big Brother, just an individual protecting him/herself.
However, it just occurs to me while typing this that some might then accuse the teacher of secretly filming children.
Hmm
maybe it's a no win situation.