A merican teenagers perform considerably worse on international assessments of achievement than do teenagers in other high-income countries. This observation has been a source of great concern since the first international tests were administered in the 1960s (for example, Dillon, 2007), not least because of the correlation found between these test scores and economic growth (Hanushek and Woessmann, 2007).But does this skill gap persist into adulthood? In this paper, we examine this question using the first international assessment of adult literacy, conducted in the 1990s. We find that, consistent with other assessments of the school-age population, U.S. teenagers perform relatively poorly, ranking behind teenagers in the twelve other rich countries surveyed (in descending order of achievement): Sweden, Finland, Switzerland, the Netherlands, Norway, Belgium, Germany, Denmark, the United Kingdom, Ireland, New Zealand, and Italy. By their late twenties, however, Americans compare much more favorably to their counterparts abroad: U.S. adults aged 26 -30 assessed at the same time using the same test ranked seventh in this group of countries, and the gap with countries still ahead was much diminished.After establishing these findings, we explore the role of higher education in this test-score improvement. We find that countries for which the age profile of test performance is relatively steep, such as the United States, have relatively high rates