After several years of slow growth, the percentage of Americans earning a bachelor's degree or higher has surged in the last five years, the result of both higher enrollment and improving completion rates. That's according to the National Center for Education Statistics, a research division of the Department of Education, which released a comprehensive report last month on the state of U.S. education.

The latest statistics show 33.5 percent of Americans ages 25 to 29 had at least a bachelor's degree in 2012, nearly a ten percentage point improvement since 1995, and evidence that U.S. students are rising to the challenge of a new technology-driven economy. As the New York Times reports today, the increase in college degree attainment has happened across the board, with strong growth among women and minorities in particular.

But don't break out the champagne just yet. Although the headline numbers on rising degree attainment reflect significant improvements in college access (if not affordability), the U.S. continues to be outpaced internationally. After decades of leading the world in higher education, the United States now ranks ninth in the proportion of young adults enrolled in college, and has fallen to 16th in degree attainment—suggesting that while graduation rates are improving, the drop-out rate remains far too high.

The deeper you dig into the NCES data, the more it looks like U.S. educational outcomes have stagnated relative to the rest of the developed world. While the percentage of the U.S. population with a high school or college degree is consistent across age groups (indicating that younger generations of Americans are not surpassing their elders' educational level in any signficant way), the percentage of degree holders in other advanced, OECD countries has been rising with each successive cohort.

For a long time, the United States has enjoyed an educational advantage over the rest of the developed world—beginning with the 1944 G.I. Bill, which allowed millions of returning servicemen to go to college after the Second World War. But the nations of Europe recovered, and set about developing their own progressive democratic states focused on educational mobility. In many ways, those educational systems—along with those of rising Pacific nations like South Korea and Japan—have now surpassed that of the United States, especially in their affordability.

If the latest NCES data is any indication, many OECD countries have already reached educational parity with the United States. Without more effective policies to bring down costs and boost graduation rates, the U.S. could find itself below the OECD average within the decade.