Case in point, a PIAAC report back in 2013 said that only 9% of the US adults were considered proficient in math and complex reasoning. And the questions used by PIAAC were arguably just high-school level. Anecdotally, how many people have heard their professors or high-school teachers complain that most students couldn't even really grasp linear equations or distributed property (students can remember rules and pass high-school test, but many of them would be hopeless if they were to pass national entrance exams in other countries).