By the very nature of Shanghai there is tons more selection going on than in any US state.
1. Incredibly high land prices 2. long history of smart/rich people moving to the city - if you fail, you go back to your hometown 3. legislation trying to push people out of the city (only overcome by smart/rich people) 4. delayed puberty compared to average white or black american 5. no cultural value assigned to being rebellious
What percent of the US students tested were non-native speakers? What percent had spent years of their education overseas?
Finally, I don't know why everyone always talks about average education levels. I would much rather have the best top 10% or 1% in any field living in my country than have the highest average. And that's why I still feel pretty good about the US.