Regardless, as far as use of CP in schools is concerned, I see a few problems with it. First and foremost is, I've met some public school teachers in my day whom I wouldn't trust with talking to my child after class, let alone administering corporal punishment. Second, the teacher's role in disciplining a child really should be maintaining order in the classroom, not really dolling out justice, and I don't think CP is the only viable way of doing this.
More generally, CP a) doesn't teach the kid why their behavior's wrong, it just teaches them not to get caught, and b) it can potentially teach them a number of other not-so-nice lessons, such as "violence is an acceptable solution" or "don't trust mommy and daddy", or even "resent and hate authority figures". These problems are especially propounded, I believe, in a classroom setting.
Like I said, there's other ways of achieving the same goals without risking the other not-so-nice lessons being learned. That's why I object to corporal punishment in general, and particularly in a school setting.