Dismissing Latvia and Estonia as racially homogenous outliers ignores the significant ethnic Russian population (in the neighborhood of 1/4 of the population in Estonia, a few percentage points below the combined share of blacks and hispanics in the US).
This group is very much a marginalized community - a study conducted a few years ago estimated that 50% of them are barely integrated or not at all - and yet these countries have performed quite well on the PISA nonetheless.
http://www.worldaffairsjournal.org/article/russians-estonia-twenty-years-after
If PISA scores are a flawed benchmark, here’s another. 14% of the US population is illiterate - with the rate among high school graduates closer to 19%.
http://www.statisticbrain.com/number-of-american-adults-who-cant-read/
We certainly have a good education system, but when discussing high school graduates a small dose of humility wouldn’t hurt. I often hear friends and distant family members make the claim that our K-12 education system is the world’s finest. The above statistics suggest it isn’t, just as our health-care system isn’t the world’s best (another common belief) nor was it any better before the passage of the Affordable Care Act.
I make this argument not because I want to bash the US, but because the first step to solving a problem is admitting that it exists, and many people aren’t there yet.