40% of American adults can't do basic arithmetic[0], which seems like a disaster to me. 88% are apparently incapable of doing things like reading a simple table or comparing two documents and identifying sentences that express the same ideas between them[1][2]. Over 50% apparently can't scroll through a list of information about books and identify the author of a specific book they're told to find. I'll never forget that in 12th grade I took non-AP government, and we were still spending significant time going over the three branches of government again (I'm quite sure this was covered in elementary school) and somehow people were not getting 100% on everything. Other tasks included--not joking--coloring pictures of animals, which the teacher put up around the room.
My school was actually rated decently for the area. Not the best, but pretty good.
I guess it depends on how you measure it. If we go by percent of kids meeting the standards and a passing grade being 70%, you could justifiable say the schools are horrible on average.
I'd bet a lot on parents caring more about their kids welfare than regulators.