Are there bad teachers and bad schools? Are there bad parents? Yes. A bad parent or even a good parent who home-schools but is ignorant - or worse, willfully ignorant will have a negative impact on their child and the child will have no other, positive inputs on their education.

As far as pervasive liberal bias? Schools are under continuous (even prvasive!) attack by social conservatives - as evidenced by the recent fight here over science standards. Parents had a teacher fired for “witchcraft” this past year (which consisted of card tricks). All in all schools have survived their acid bath very well in the face of mendacious behavior and inadequate funding.