I definitely see that the curriculum is tougher at the middle schools than back in my day. It just seem to me that a lot of skills/knowledge are pushed down into the lower grades but by the end of high school, there generally isn't a whole lot more to show for it.
It would also be clearer if the curriculum is more uniform so that the same names actually mean the same topics. It wasn't until I had a discussion with DS' algebra teacher that I realized there is such huge variations in just the coverage for Algebra I. Interestingly, I found one document online that references our district's AP Calculus AB course as Calculus I, II and our AP Calculus BC course as Calculus III with the idea that a student could place out of the first three semester of college Calculus whereas AP Calculus BC is traditionally a test on mastery of topics covered during the first two semesters of college calculus.
I wonder if the AP World scores are relatively low because the test takers are predominantly Freshmen or Sophomores rather than Juniors and Seniors.
