Not only did many industrialized countries outperform the United States in science on a recent international exam, but American students' academic achievement was also more likely to be affected by their wealth or poverty and family background than was their peers' in higher-scoring nations. That was one of several sobering findings for the United States included in the results of the 2006 Program for International Student Assessment (PISA) released this week. The program showed U.S. students lagging behind a majority of participating developed nations in both science and mathematics. But test results and the accompanying study also appeared to show another trait of the U.S. education system, one that, in theory at least, seeks to provide equal opportunity for all students, regardless of economic circumstances. The results of the test, given to 15-year-olds in 57 countries, including 5,611 U.S. students, show that an estimated 18 percent of the variation in Americans' science scores were related to students' socioeconomic circumstances, as measured by the PISA. That proportion was significantly higher than the average--about 14 percent--among industrialized countries. And the socioeconomic variation was more than twice as high as that of several of the highest-performing countries in science, such as Finland and Canada, where it hovered at about 8 percent.