Some early math suggestions

That's an interesting list you have there. I am an adult learner who actually went through all of the elementary, middle school, and early high school math topics here while I was working up the courage to relearn calculus (which I am finally doing now). I recognize several things on your list that I learned in elementary school (kindergarten in 1957-58 through 6th grade in 1963-64) but now realize I didn't see in Khan Academy, such as Roman numerals, number words, cardinal vs. ordinal numbers, and reading a calendar. I remember learning a lot of calendar stuff in 1st grade, although I learned about leap years from my father once when we were waiting for a traffic light to change at a busy intersection.

Another thing I learned a lot about in school, all the way through 9th grade, but didn't see much of on Khan Academy, was sets. Just about every math subject I took in the early through mid-1960s had a segment about sets. I later learned that what we were being introduced to in that time frame in the U.S. was something called "new math". I recently read a Wikipedia entry about "new math" that said that this quickly fell out of favor and by the 1970s was no longer being taught. And the study of sets was a big part of "new math". I noticed that Khan Academy does have some more detail on sets and set terminology in either the Statistics and probability or Advanced Placement Statistics course (or both). That's pretty far advanced from where I learned it while growing up.