I get one of those eternally stupid villagers once in a while, but it's never an overwhelming problem. Sooner or later they get to Master. It doesn't matter how many lifetimes it takes them, does it?

One problem with the Parenting skill is that if you set too many villagers to Parenting, they interrupt each other all the time and no one ends up learning anything at all. I usually only set one or two villagers to Parenting at a time.