You can see this in high school test scores, in placement exams, in Freshman college performance, and even in new grad hire cohorts.
The autodidact set has realized that they can teach themselves a lot of what they would've learned in coursework at colleges. There are still some elite career pathways where formal education is necessary, but an autodidact who doesn't want to follow one of those career pathways now knows that they can go without.
American colleges provide a useful-if-overpriced service to non-autodidacts, but their product is not ready to deal with students who are YEARS behind in their formal education.