Nope. I'm mostly a--
well, I guess I'm a post- Evangelist in this sense. LOL.
I've learned over the years that there are some people who can get it, some people who WILL get it if you lead/guide them, and then there are people who either cannot get it (they simply lack the capacity to truly understand) and those who WILL NOT (because it violates their belief system and cognitive dissonance is so uncomfy).
A surprising number of educators are in the last two camps.
They cannot be reasoned with. Only avoided and detoured around.
There are also those who-- like your son's math teacher-- are in that latter camp but have some peculiar selective blindness re: genuinely HG+ children. We've run into them, too. Honestly I don't rock their world, as much as I would like to. Generally I've discovered that if you PUSH them to accept what they aren't ready for, it backfires and then snap back to a more rigid stance with your own child instead.
I need the cooperation too much, basically. So I leave them alone, they give DD what she needs, and we all go on about our regular business.
