In the middle of the 20th century, the US economy had the enormous advantage that its workforce was by far the most skilled in the world. That advantage has largely dissipated. Alexander Monge-Naranjo of the St. Louis Fed provides some basic facts in the short article "Workers Abroad Are Catching Up to U.S. Skill Levels" (Regional Economist, Third Quarter 2017, pp. 6-7). The underlying data here is from Robert Barro and Jong-Wha Lee, "A New Data Set of Educational Attainment in the World, 1950-2010," Journal of Development Economics, 2013, Vol. 104, pp.184-98.

Here's a comparison for 1950, showing what share of the workers in each country are in a given education group. The US is the light blue bars on the right of each cluster. Notice that the light blue bars are typically lower in the lower education categories, but higher in the higher education categories. Also, if you do a bit of mental addition, you see that countries like France, Germany, Japan, and South Korea had two-thirds or more of their population in the broader category of "primary school education or less" circa 1950.

The next comparison is different in two ways. It looks at data for 2010, and it focuses only on workers in  the 25-35 age bracket. By leaving out older workers, the focus is on what education level workers are likely to have in decades ahead. The light blue bars showing the US levels of education have clearly risen, but the other countries are now much more similar. Even in cases where a country like Germany looks lower in college degrees, it's worth remembering that Germany has an aggressive and far-reaching apprenticeship program that help to provide future workers with job-related training. One can of course raise the possibility that those South Korean college degrees might not be equal in quality, on average, to US college degrees. But the size of the changes is so enormous that quibbling over quality is not going to alter the main pattern.

The catch-up in education levels is also apparent, if not as pronounced, in emerging market economies. Here's a similar figure, for workers age 25-35 in 2010, comparing the US to emerging market economies of Brazil, China, India, Mexico and Russia.

I suppose there are a few themes to draw from this.

First, catch-up in education levels by the rest of the world is broadly a good thing, because it's a good thing for a range of reasons from economic to self-determination when more humans have a higher level of education.

Second, 1950 was a unique time, and it's implausible that the US would have maintained its status of dramatically higher education levels indefinitely.

Third, with those previous points acknowledged, the US has not done a good job in the last half-century of fostering the incentives, institutions, and culture that would have helped it to keep a lead in human capital. I'm not talking only or even mostly about the public schools here, but about the many contexts in which schools, colleges and universities, employers, and individuals make decisions about providing and working on their education.

Those interested in more details about the ongoing loss of the US position as the clearcut world leader in an educated workforce might be interested in a couple of previous posts: