It's almost an article of faith these days that students in the United States lag their peers in other industrialized countries in reading, math and science. The conclusion many draw is that American schools are "failing" and, therefore, policies should be directed toward fixing what is considered by many as a broken educational system.

But a new study by researchers at the Economic Policy Institute, a non-partisan think tank, challenges that assumption. By sifting through data from international test results, breaking down scores by social and economic classes, they offer a different picture that suggests American schools are doing much better than they're given credit for.

"What do international tests really show about U.S. student performance?" by Martin Carnoy and Richard Rothstein, compares American students' performance over time on international tests with three top-performing countries (Canada, Finland and Korea) and three similar post-industrialized countries (France, Germany and the United Kingdom).

Using scores from the Program for International Student Assessment, or PISA, exams, they find the "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."

In addition, they argue, those tests over-sampled American students from lower income households, compounding the effect of class and income bias. If the sample of U.S. students taking the 2009 PISA test is adjusted to more accurately reflect the total population, the United States' ranking in the world would increase sharply: from 14th to sixth in reading; and from 25th to 13th in math.

Moreover, if students are compared on a class-to-class basis with their economic peers in other countries, U.S. students score better in reading than disadvantaged students in France, Germany and the U.K. They score about the same as their economic peers in those countries in math.

Furthermore, scores for disadvantaged students in the U.S. have been improving over the last 10 years, possibly the result of No Child Left Behind and its intense focus on closing achievement gaps.

Still, across the class spectrum, U.S. students performed worse - and in some cases substantially worse - than their economic peers in the top-performing countries of Canada, Finland and Korea. Adjusting for the sampling error narrows the gap some, but not much.

The authors do not argue that it's OK to have achievement gaps, or that schools have no role in trying to close them. Nor do they argue that economic injustice is the root of all problems in public schools. These guys are not the Occupy Wall Street crowd.

But they do argue that policymakers need to be cautious about using test score data and avoid the temptation to leap to conclusions or assign blame.

"We are most certain of this," the authors write in their conclusions. "To make judgments only on the basis of national average scores, on only one test, at only one point in time, without comparing trends on different tests that purport to measure the same thing, and without disaggregation by social class groups, is the worst possible choice. But, unfortunately, this is how most policymakers and analysts approach the field."