[tokenadult]

Backing up what you said, where the United States really falls behind in international comparisons is in direct comparison of students from prospering families, or comparison of students who have college-educated parents. See

http://www.hks.harvard.edu/pepg/PDF/Papers/PEPG10-19_Hanushe...

for considerably more detail. The United States has a much lower top end of achievement in its population distribution than most other OECD countries.