Why did the United States become the leading economic power of the 20th century? The best short answer is that a ferocious belief that people have the power to transform their own lives gave Americans an unparalleled commitment to education, hard work and economic freedom.

Between 1870 and 1950, the average American’s level of education rose by 0.8 years per decade. In 1890, the average adult had completed about 8 years of schooling. By 1900, the average American had 8.8 years. By 1910, it was 9.6 years, and by 1960, it was nearly 14 years.

As Claudia Goldin and Lawrence Katz describe in their book, “The Race Between Education and Technology,” America’s educational progress was amazingly steady over those decades, and the U.S. opened up a gigantic global lead. Educational levels were rising across the industrialized world, but the U.S. had at least a 35-year advantage on most of Europe. In 1950, no European country enrolled 30 percent of its older teens in full-time secondary school. In the U.S., 70 percent of older teens were in school.

America’s edge boosted productivity and growth. But the happy era ended around 1970 when America’s educational progress slowed to a crawl. Between 1975 and 1990, educational attainments stagnated completely. Since then, progress has been modest. America’s lead over its economic rivals has been entirely forfeited, with many nations surging ahead in school attainment.