I haven't worked in an american classroom, but as a math educator, thought the CommonCore looked great when it was first rolling out.
Math education is (kind of strangely) a bit of a battlefield in the US (maybe not so strangely, when everything else seems to be, too)... I think a big part of it is prevalent math anxiety - perhaps embarrassment at seeing unfamiliar things on the kid's homework. Along with this, there's still lingering bad PR from the 'New Math' of the seventies, which made it somehow acceptable to make the argument that we should stick to teaching math the same way forever. (Especially for people who believe that math hasn't changed since Newton.)
Agreed, I can't stand the way we teach math in the US. I love math enough to have accidentally gotten a minor in it, but especially high school does nothing but train kids to hate math. My calculus class in high school was a net negative, since teaching to the test just caused many of my friends to switch away from STEM majors in college (if Calc 1 was that horrible, why become an engineer ahd have to suffer even more?).
One of these friends went on to become a forensic accountant, so she obviously couldn't hate math that much, but that calculus class was traumatic enough that she summarily dismissed a biology major in college. I think one of the main pain points, which my dad was able to tutor me through, was understanding why. Learning calculus (or any math, for that matter) as just a list of mechanical steps is awful, whereas learning why we perform the mechanical steps allows one to glimpse the beauty behind math. I wonder how many children we've ruined this beautiful subject for?
Math education is (kind of strangely) a bit of a battlefield in the US (maybe not so strangely, when everything else seems to be, too)... I think a big part of it is prevalent math anxiety - perhaps embarrassment at seeing unfamiliar things on the kid's homework. Along with this, there's still lingering bad PR from the 'New Math' of the seventies, which made it somehow acceptable to make the argument that we should stick to teaching math the same way forever. (Especially for people who believe that math hasn't changed since Newton.)