Carnoy and Rothstein delved into databases from the Program for International Student Assessments (PISA) and the Third International Mathematics and Science Study (TIMSS), disaggregating test scores by students' social and economic characteristics, school composition and other criteria.
"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," the scholars said.
"Because social class inequality is greater in the United States than in any of the countries with which we can reasonably be compared, the relative performance of U.S. adolescents is better than it appears when countries' national average performance is conventionally compared," they said.
If corrected for social-class distribution, average U.S. reading scores would be higher than averages in France, Germany and the United Kingdom and average math scores would be about the same as such places.
Even so, U.S. students still would lag top-scoring Canada, Finland and Korea, they said.
"At all points in the social class distribution, U.S. students perform worse, and in many cases substantially worse," than students in those countries, Carnoy and Rothstein said.
"Although controlling for social class distribution would narrow the difference in average scores between these countries and the United States, it would not eliminate it."
The two said that policy conclusions drawn from the international studies are often "oversimplified, frequently exaggerated and misleading.
"They ignore the complexity of test results and may lead policymakers to pursue inappropriate and even harmful reforms.
"A careful analysis of the PISA database shows that the achievement gap between disadvantaged and advantaged children is actually smaller in the United States than it is in similar countries," they said.
"The achievement gap in the United States is larger than it is in the very highest-scoring countries but, even then, many of the differences are small," they said.
Their report is posted on the Economic Policy Institute website, www.epi.org.
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