I found this hilarious, for a variety of reasons, none of which I'm going to disclose.
Provocation, of course, is only a defence to murder. And even then, it's only a partial defence (ie, if accepted, it reduces the charge to one of manslaughter, which is significant, because murder carries a mandatory life sentence, whereas sentencing for manslaughter is discretionary).
Teacher attack boy 'was leading light behind trouble'
Does what the kids did look clever, or admirable? Did it have a purpose outside the somewhat trivial objective of humiliating authority figures? Was the teacher's response proportionate, given the effect that the kids' behaviour had on him? Did the school understand the psychological impact that the behaviour of these kids had on its teachers? Did the school do anything about it? Was it capable of responding, even supposing any of the teachers were able to acknowledge that they couldn't handle their classes, and sought help?
So many questions. None of which are likely to be answered.
My personal analysis is that, based on what is in the piece cited, none of these kids had assessed what it was that they didn't like about this teacher (if, indeed, they disliked anything), such that they would humiliate him. Even supposing they had made some kind of assessment, none of them were brave enough to front it out, one-on-one - they sought safety in numbers. The question of whether their motivation for humiliating their teacher was valid simply doesn't come into play.
I think that they perceived he was vulnerable, and then they proceeded to make that true, by their conduct, and they kept going, until they found something that "worked" (ie, Mr Harvey reacted in a way that they found amusing). They did this, because they perceived that Mr Harvey could do nothing about it, I think. And they were right, weren't they? How wonderful it is, when we can prove our points, in this way.
On second thoughts, I think even this is too complicated. The kids did what they did, because they thought it was appropriate, in all the circumstances. In other words, it was their pattern. And Mr Harvey, he reacted to the stimuli he was subjected to in the way that he did, because that was the only thing that he could think of - and can one honestly say that one would not have done the same thing? Liars. I would have, except I'd have done a better job of it.