The above mentioned tests (TIMSS) is a 20 year study involving
4th and 8th graders - not high schoolers taking AP classes. I'm assuming that they pick them at random (as opposed to sending their best and brightest - this isn't Math Olympiad). You can see that the gap between the East Asian kids and the next highest country in 4th grade was
23 in 2015 unchanged from 2011. However, the gap between the East Asian kids and the next highest country in 8th grade is
48 in 2015 increasing from 31 in 2011. My take from this is that the gap between East Asian kids and the rest INCREASES as the grades get higher.
http://timss2015.org/timss-2015/math...t-achievement/
http://timss2015.org/timss-2015/math...t-achievement/ (click on Grade 8)
I think that (on a whole) US kids are okay in the younger grades (addition/subtraction/multiplication/division) but somewhere around 3-5th grades when they're supposed to be learning fractions, decimals, and percentages - things get a bit fuzzy and because there are sometimes gaps or concepts aren't mastered, the kids get more and more confused as the grades get higher. Sorry, but I'd place my bet on the average East Asian kid than an average American every day and twice on Sunday when it comes to math - they know their stuff.