I rewatched this not that long ago, and even though I know it's pretty standard to watch comedies from this era and see a lot of things that are like 'wow that didn't age well' (even if it's still an otherwise funny movie), but rewatching this, I was surprised at how the overall messaging and way it depicts these characters felt a lot more fair and interesting than a lot of other films from that era.
Particularly, the scene where Jack Black takes the principal out to get drinks and we see a totally different side of her, as well as when we see the barrage of parents harassing her and suddenly we totally get a sense of how this kind of pressure could lead to someone becoming like this. I feel like the trope of 'the stuffy old mean teacher lady' has been a comedy thing for about as long as there have been movies set in schools, but this one just flips it on its head in a way that really stood out to me.
It also does a really good job at avoiding the overly cartoony cliche ending of "oh, but look what they learned! it's totally fine!" I mean, yes, it does that somewhat with the very ending over the credits, but the parents are still very rightfully furious that this random stranger has been with their kids, and the movie treats it more like how I expect people would react to it in real life. It's a tiny thing, but just giving these elements (such as the principal or the parents reactions) a little more believability and less cartoonish one dimensionality really adds to it.
I'm also glad they never did a sequel, because there's absolutely no reason to, although now that I've said that I'm assuming we'll see a headline that it's been greenlit within the next two days.