Why not? They've already made such a direct comparison. You take the exact same math or science questions (or you could even issue a subjective test on civics, history and reading/writing) and you issue them to two samples of students, one from the states and one from a European class. Both have to be relatively the same in regards to performance relative to their own country. I've seen one such study that compared the test results of one classroom from one of the best performing schools in New Jersey versus the test results of one classroom from one of the best performing schools in a province of Denmark. The test questions were identical. Guess who scored higher? There are numerous such studies comparing relatively similar classrooms in the U.S. to those in Japan, Korea, and other parts of Europe. There is no question that we, as a nation, are lagging far behind in math and science. I imagine it is true for the soft sciences as well, given that foreigners know more about our own history than we do.