I'm a big fan of Singapore math. The countries that score top in the world on primary math education use it. In basically every research study that has been done, it works. 3/4 of my children were lucky enough to go to a school that taught it, and it worked well for them.

Unfortunately the US approach has been to throw out every research study suggesting it might work, while failing to fund better studies. See https://ies.ed.gov/ncee/wwc/Docs/InterventionReports/wwc_sin.... Behind this is that fact that the educational establishment makes a ton of money off of rewriting textbooks and retraining teachers for each reform wave. The hasty changes are guaranteed to lead to disaster, which motivates the NEXT reform wave, which they then also profit on. My mother became a school teacher in the 1950s, and this cycle was ALREADY in progress back then. (Think Sputnik leads to New Math leads to Why Johnny Can't Add, etc.)

Switching to already existing books for an approach that actually will work would be a disaster for the education establishment. And so we'll never do it. No matter how embarrassing our regular (but profitable for the education establishment) disasters are.

I complain about this occasionally. See https://news.ycombinator.com/item?id=13822577 for a more general complaint, and https://news.ycombinator.com/item?id=34634210 for a rant about the Common Core disaster specificially.