Even so, the U.S. 9th graders still scored better than Germany, Denmark, Canada, and The Netherlands. Those scores included ALL ranges of socio-economic classes for the U.S. and only the top 2/3 or so of those countries.
In the event one would want to look up this study, I give the following information.
Elley, W. B. (1992). How in the World do Students Read? IEA Study of Reading Literacy. The Hague, Netherlands: International Association for the Evaluation of Educational Achievement. Excerpts of this study may be found in the book, What Really Matters for Struggling Readers by Richard L. Allington.
So all that being said, U.S. kids stack up just fine across the world. Does that mean we can't and shouldn't do better? Of course we should.
English readers do well on average but have more people in the lowest category, usually "functionally illiterate" than foreigners.