Courtesy of The Peter Principle, which, it should be noted, was written in 1969:
"So, to avoid the accumulation of incompetents, administrators have evolved the plan of promoting everyone, the incompetent as well as the competent... The result of this wholesale percussive sublimination is that high school graduation may now represent the same level of scholastic achievement as did Grade 11 a few years ago. In time, graduation will sink in value to the level of the old Grade 10, Grade 9, and so on." p. 158
Bear in mind that the home-schooled child receives an equivalent high school education in a mere nine years. Part of it, no doubt, is to the superiority of the method. But it is difficult to underestimate the degree of enstupidiation foisted upon the nation's youth, courtesy of the government run monopoly known as the public school system, funded by the tax dollars of the American citizenry.