I have been Corresponding with Kevin Drum

The question is whether poor US performance in international standardized tests doesn't prevent the US from excelling in some fields because it reflects the low scores of the least successful test taking students in the USA, while excelling depends on how much people near the top of the distribution know. Basically all of the international comparisons of student achievement suggest that this is partly true. The best students in the USA do OK (not as well as in some countries many of them in East Asia but OK).
The least successful at test taking (SATT) students in the US do much less well than the least SATT students in other industrialized countries.

For example, look at table 2.1a in the report on the PISA 2006 study

it gives numbers of students above more or less arbitrary thresholds. The fraction of US students in the top group is tenth best in the OECD. Not great but not horrible either. The fraction of US students in the bottom group is third from worst. The US outperforms Mexico and Turkey.

Our problem is that some schools in the US just don't work. Of course even George Bush knows that.