Comment by troupe

That may be less true than it was 20 years ago. Even free resources like Khan Academy can go a long ways in helping parents educate their kids beyond what they know themselves. And for parents willing to spend even a fraction of what the public school would spent on education, they can pick and choose curriculum, tutors, or even online live classes with teachers well beyond what they would have in their local high school.

That said, parents without much of an education themselves may tend to set the bar too low for their children, but that often appears to be an issue in the public school as well.