Considering all the inner city schools that contribute to the average, it is no surprise that the US is not in the top 10. Multiculturalism has its price, a high one. But look at the bright side, all those kids from other countries, can now come to universities in the United States for cutting edge mathematics and science. ...Meanwhile, a large number of US students who would like to be in our best universities can’t be because they are victims of our mass education fiasco that drags the top down to the bottom in the name of fairness.
Factor in the rot that infects just about every metro school district in the US. Those results tend to bring down the US average. Throw them out and the US is easily in the top 10.