Children aren’t a blank slate when they get into school. Genetics, parenting, and culture all have an effect.

That said, the fact that teachers that make tenure basically can’t get fired for lack of performance is ridiculous. Imagine if you just had to be a good little coder for a few years, and after that as long as you put any amount of effort in at all you wouldn’t lose your job.

I certainly had teachers growing up that were terrible at their jobs. I also had some that were pretty good. Most were mediocre to the point where I don’t think they’d stay employed in a regular non-union type job. At the very least they wouldn’t be getting performance raises.