This is all generalized - first the overseas comparison isn’t apples to apples while we require 100 percent to attend high school overseas does not (Japan for instance youneed to test into high school and your family pays more or less depending on which one you get into and not all go so your already comparing the top tier to our complete body when it comes to test scores). Second the level of math is dependent on a number of factors including: family district and teacher. My daughter is a freshman and will start calculus next year - they kicked her into algebra in fifth grade to which my jaw dropped since I first saw it in eighth (back in the day). Now are all her peers in the advanced class no, but they have all seen algebra by 7th grade in the district before the advanced kids did when I attended. Anecdotes exist of failures in certain areas sure but you don’t set national policy off anecdotes.
Except in the USA!