That's the kind of thing you could get away with legally because it all appears to be truthful. The kids in this case, according to the article, made two HUGE legal mistakes: they structured the web page to look like the assistant principal herself posted it and they included a directly false allegation that she was a lesbian. If high school kids are going to post derogatory material about their teachers and school administrators without running afoul of the law, they have to keep it to provable facts and opinions.
Ok, since you seem knowledgeable about this. What's to prevent them from doing all this anonymously? If they can keep their mouth shut and do all there enterring through a library computer or some other more or less public terminal...would it ever have been traced back to them?