Their educators became respected professionals who had to prove themselves before becoming educators.
Might be the time to bring up Amanda Ripley's book where she investigates this indepth by comparing both exchange students to the US and exchange students from the US to other countries.
https://www.amazon.com/Smartest-Kids-World-They-That/dp/145165443X/ref=asap_bc?ie=UTF8
I'm not saying there aren't benefits to extracurricular activities, but it's an objective fact that the US ranks below many other industrialized nations in academic achievement. An analysis of these other country's school systems shows they place greater emphasis on academic rigor and less emphasis on athletics. Texas' "Friday Night Lights" culture is an extreme example of this. These small Texan towns live for football, kids and parents alike, with academics being secondary.
If you want to learn more about the educaitonal cultural differences between US and other high-performing countries I recommend this book:
https://www.amazon.com/Smartest-Kids-World-They-That/dp/145165443X
The biggest difference is that in China (and actually, most other countries around the world) curriculum policy is set nationally by the government, and thus the sequence of courses students take in high school is remarkably standardized from place to place. In China (as also in Japan and South Korea) upper-middle-class and wealthy families will supplement this with an extensive system of private cram schools and tutors that are meant to help their children get a competitive edge on college entrance exams. But the schools themselves are very consistent in terms of what is taught and how. Their national high-school curriculum also puts a heavy emphasis on mathematics and science, and less of an emphasis on humanities-based subjects.
In America, by contrast, there is no national curriculum (Common Core is attempting to change this, but with limited success thus far). States are free to set whatever curriculum and graduation standards they want, and even at the district level course offerings tend to vary widely. They also tend to correlate strongly with the wealth of the school district-- an upper-class community will tend to have many students taking accelerated courses at a much higher level than in a comparable Chinese school, while a school in a poor district may not even offer Trigonometry or Pre-Calculus in high school. So when you read that American schools are much easier/less rigorous than other schools internationally, this aggregated claim covers up the fact that this it depends completely on the wealth of your district.
If you're interested in differences between the U.S. education systems and other countries, a book you might want to check out is "The Smartest Kids in the World" by Amanda Ripley. (Amazon link)