Actually this isn't quite true. Americans are getting less educated every year however which puts the blame largely on the public education system, which is where most Americans get educated. So to speak.
When I was in High School, ignoring the hardships of actually getting to the building, and took a math test, you were expected to produce the right answer. Methodology was taught, but if you wanted to use a Ouija board for a calculator, that was fine. We were also expected to be able to calculate the odds of the Ouija board delivering the correct answer two times running. Trust me; There are a lot of zeros to the right of the decimal point before you come to the first actual number.
My brother, who came 2 years behind me, got what was called "New Math". Using this technique, you didn't need the right answer as long as your methodology was correct. I went on to design missiles. He became an economist. Case closed.
In his defense, he quickly gave up on economics and become a successful businessman. As such, he probably now has a better grasp of how things actually work than Paul Krugman.
Americans also get dinged for not being as multilingual as say the Europeans. Back in the day this was because if you wanted anything, we probably made it better, faster, and cheaper than any one else. It helped that we were the only country in the world that hadn't been recently been bombed back to the stone age. Foreign language wasn't necessary. Everyone was learning English.
Today, if you want something, you come to America, and we'll tell you precisely which country to go to to get your product properly designed and built. What the unions did for manufacturing, they are now doing for education.