If your kid has failing grades throughout his high school career, but getting social promotions, how can you assume he is doing alright. If you do not have enough passing credits to graduate with a high school diploma, you don't have enough credits.
Public schools keep the private schools thriving.
Especially the ghetto public schools.
I think it is a parental thing. Been observing a lot of public school zoom classes while my grandkids have been doing distance learning. Teachers have been fine. Instruction has been fine, in some cases actually impressive in the case of our second grade grand daughter. Of course we and our kids are not the type to assume everything is OK if one of the kids isn't cutting it. Quality may change from place to place, but the biggest thing is the kid doing the work. If they won't and you don't get on top of it for any reason, you and the kid are screwed. The problem is the modern failure of parenting, not shitty teachers being turned out by the colleges and universities.