[WS:] The problem with international comparisons of this kind is that they tend to compare apples and oranges. The US has compulsory K12 education, most other countries do not. which means that we are not comparing similar populations above the 7th or 8th grade (the general population in the US vs college bound subset of general population elsewhere.) Researchers are probably aware of that, but such subtleties almost never make it into press reports, especially when the results serve the political agenda of the education "reform" crowd.
Based on my personal observations, the US has many shortcomings, but its educational system is not among them. In my opinion, the US has probably one of the best educational systems in the world ("reforms" and standardized testing notwithstanding.) The problem is not with the schools but with the population of students attending them, or rather obstacles to learning they face, ranging from family background, to living conditions, to job opportunities, and to anti-intellectualism and anti-institutionalism deeply embedded in the US culture.
Wojtek