I agree with you that the difference in standards of living is fair game. It strikes me as somewhat disingenuous to say "well, assuming that unsavoury crowd over there wasn't dragging down our scores..." and that is what the review appears to be trying to do in some respects.
But check out the things in the "also noted" summary:
There is an achievement gap between more and less disadvantaged students in every country; surprisingly, that gap is smaller in the United States than in similar post-industrial countries, and not much larger than in the very highest scoring countries.
Achievement of U.S. disadvantaged students has been rising rapidly over time, while achievement of disadvantaged students in countries to which the United States is frequently unfavorably compared – Canada, Finland and Korea, for example – has been falling rapidly.
But the highest social class students in United States do worse than their peers in other nations, and this gap widened from 2000 to 2009 on the PISA.
U.S. PISA scores are depressed partly because of a sampling flaw resulting in a disproportionate number of students from high-poverty schools among the test-takers. About 40 percent of the PISA sample in the United States was drawn from schools where half or more of the students are eligible for the free lunch program, though only 23 percent of students nationwide attend such schools.
So it seems the point is that we actually aren't doing as badly as some like to insist, and that the future isn't quite so gloomy. Well, neither of those are resoundingly optimistic statements, but hey.
