My cynical view is that New Math, like Reform Math and Common Core Math later, was carefully designed NOT to work, precisely as Whole Word is designed not to work.
See the video mentioned: An Inconvenient Truth, which is about Reform Math but shows you how a program can be designed not to do what it’s supposedly designed to do.
Here is an article titled “The assault on math,” making the same points.
http://www.improve-education.org/id60.html
See # 21; many teaching “methods” today are designed to accommodate the teachers who primarily come from the bottom of their college classes. In my experience, parents are expected to teach their children today because teachers are ignorant/uneducated. When children routinely are assigned homework that hasn’t been covered yet in class, and steered towards websites for extra help, it is very clear that the teachers don’t know the material - the parents or a website will provide the teaching.
I’ve posted on other threads that if your child is not in an “honors” track (”average” from thirty years ago), then he/she has already been written off and will receive no education at all. The schools determine who has involved parents, and focus on those students.