Someone up thread seemed to think the average student of another country would blow away the average US student. I don't think this is true. The US pays lip service to universal education more then most other countries. Unfortunately we don't follow through on it and this leaves a large enough number of substandard schools to make a significant impact on US test averages. The sad fact is the tail end of these averages are so bad they bring down the score, but the "average" for the majority of US students is much higher.
This stratification of education is probably a significant contributor to the stratification of wealth in the US, and it's not OK.
I am assuming you are talking about K12 education. That is pretty absurd.
California currently spends about 10k per student for public education. That makes 30k sound crazy, but in 1970 California spent 5500 which is about 35k in 2017 dollars. California (and most of the US) is woefully underfunding it's schools.
[1] https://www.cato.org/publications/policy-analysis/they-spend...
This is certainly not my experience of the US public school system, either as a student or a parent. The typical US school has always cared more about getting 20th-percentile students to meet a minimum standard. And if the student makes an effort to work with the school, the school is very good at it. Public schools are evaluated based on how many students meet that minimum standard ("No Child Left Behind"), and they respond to that incentive.
The 80th to 90th percentile students, well, they're kind of an afterthought. I mean, they're going to ace all the standardized exams anyway. Now, some public schools will make an effort to help high-performing students, because teachers do care, but it's not incentivized.
Private schools, on the other hand, are evaluated on a very different metric—how many students get into Harvard/Yale/Stanford/etc.? They game this metric by offering generous scholarships to top-notch students, and by charging stiff tuition to rich parents.
Schools in the US are locally controlled.
There are places that run schools like this. And there are school systems that have fantastic magnet schools for gifted students.
I have zero doubt that the average Japanese student blows the average American student out of the water. But the US produces both a greater number and a greater degree of ridiculously talented and driven students.
Asian countries generally have a high average and low variance distribution in students. The US has a lower average but a much higher variance and thus has more outlier students on both ends of the spectrum. Whether this is good or bad would depend on your perspective.