I will never forget when I was a high school sophomore (MANY, MANY moons ago). The math class textbook had the title:
The New Math
My immediate reaction was ‘what was wrong with the math before today?’
Fortunately, back then, no matter what the textbook might proselytize, the teachers still taught us appropriately.
Many years later, I was assigned as a long-term substitute in middle school math. When I demonstrated what my teachers had taught me, some of the students asked “why doesn’t everyone teach this way.” I remember using that question/moment to state something like ‘you and I cannot control what other people do; we can control what each of us do.’
PS Yes, middle school students are basically aliens, but they are a gas to inspire and teach.
the “new math” is nothing compared to common core math, which is so convoluted that well educate mathematically literate parents don’t understand it.