It's a lot easier for 17 million people to live in (relative) privilege than it is for 300+ million. Scale matters when dealing with tangible requirements.
I'm not sure what "scale" is supposed to indicate in this context; if you rank nations by population density then Singapore is at one end and Finland is at the other, and they both have better results than the USA. In 2011 Finnish per capita GDP was less than 80% of ours. I don't doubt they'll pass us eventually (Singapore already has), and our woeful system of elementary and secondary education is a principal reason why.
