I sadly don't know how to fix it without reworking the entire teacher education system, sadly, but I do believe it's
the problem affecting primary schools especially. How many times are you taught to read and the 'importance' of reading by a teacher who doesn't like to read themselves? Or 'science' by a teacher who has no grasp of what science is and just reads the slides (I distinctly remember having to correct my 5th grade teacher becasue the notes she used were so old it said Saturn was the only planet with rings...I was that kid, but at least it was after class!).
We need teachers who have trained in those areas, and then wanted to become teachers. And it needs to go all the way up through middle and high schools, but I truly think the focus should be on primary first. It's why we get so many kids who don't understand multiplication when they get to high school, let alone division -- their teachers don't either and they just give them calculators at a young age! And it all boils down to how teachers themselves are trained.
Back to math at the school I taught at, there are two there who understand it. Funnily enough, they both came out of retirement to teach again (one has been doing it for 15 years, and the other just retired from her VP job a few years ago), and they're related. The older one married the younger one's uncle. It's funny how it stays in the family. The younger one's dad was also a math/chem/physics teacher, and was an amazing teacher until he just got too old. They were the only teachers I know or had at that school when I was there who truly knew math, and it showed in how they taught and the general outcomes of their students -- A "C" student in the accelerated algebra II class made an easy "A" on college algebra when they got there two years later, simply because it had been imparted to them that well.