The test has only been administered since 2000, and shows U.S. students consistently hovering right around the average, at about the same achievement levels in math and reading as countries like Sweden, the United Kingdom and France. Overall, the U.S. scores are about the same as they were a decade ago, while some countries have improved.
"A better way for him to state it is to say American achievement is mediocre," Loveless said. "It's been mediocre for 50 years."
Romney also asserted that millions of students are getting a "third-world education." Looking again at the PISA test, students in schools where more than 75 percent of children were eligible for free and reduced-price lunch — a key indicator of poverty — scored an average of 446 points in reading. That's at about the same level as Chile and Serbia. Meanwhile, those in the wealthiest U.S. schools score nearly as high as the top performer, the Shanghai region of China.
ROMNEY: Students participating in the Washington, D.C., Opportunity Scholarship program made gains and "after three months, students could already read at levels 19 months ahead of their public-school peers."
THE FACTS: Romney's description of the success of the school voucher program, which helps low-income children in the nation's capital attend private elementary, middle and high schools, doesn't match up with Department of Education evaluations.
A congressionally mandated review of the program released in 2009 found that after three years — not three months — only some students saw those gains. About one-fourth of children who used the scholarship read 19 months ahead of their peers after three years. In general, however, students' gains were more modest. After three years in the program, students read at about four months ahead of their public-school peers.
A 2010 evaluation of the program found that on average, after four years, reading and math test scores of opportunity scholarship students were statistically similar to those not offered scholarships.
The program did, however, significantly improve students' chances of graduating from high school.
Associated Press writers Sam Hananel, Jack Gillum and Jessica Gresko in Washington contributed to this report.
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