International testing data are often used by those urging educational reform in the United States. Here is a recent analysis that addresses issues at a deeper level taking factors such as SES into account. Very complex:
For example:
Because in every country, students at the bottom of the social class distribution perform worse than students higher in that distribution, U.S. average performance appears to be relatively low partly because we have so many more test takers from the bottom of the social class distribution.
BUT
Disadvantaged and lower-middle-class U.S. students perform better (and in most cases, substantially better) than comparable students in similar post-industrial countries in reading. In math, disadvantaged and lower-middle-class U.S. students perform about the same as comparable students in similar post-industrial countries.