I don't think it's fair to blame a school system for failing to educate the children of a single mother on welfare as well as those with PHD's from Harvard. And I am not suggesting that it's genetic. If you took identical twins and adopted one into each of those family's I would expect to see a similar performance gap.
The US has some 'great' public schools, and some 'terrible' ones. But, the difference has a lot more to do with the students than people are comfortable admitting. The private / public gap in education is also a lot less than you might expect.
I agree, I don't think school systems deserve the blame. They're shouldering what might be considered an unrealistic burden, but this is a potentially major way to improve performance - by recognizing the differences that lie within students and getting 'single-mother-on-welfare' to perform as well as 'book mcbook III'.
The US has some 'great' public schools, and some 'terrible' ones. But, the difference has a lot more to do with the students than people are comfortable admitting. The private / public gap in education is also a lot less than you might expect.