If you remember from the original thread, I made the point that my wife, who does the bulk of the teaching at home, hated high school and barely graduated. If someone's teaching skills are limited to passing on pure information to a child, then I would agree with CholeraJoe that the best candidate is obviously the most educated. But teaching goes beyond just the transference of information from one parent (adult) to child. My wife absolutely adores children and loves nurturing them, and this "skill" is absolutely necessary in the learning process. This love is the birthplace of learning, which makes the home an ideal place for early learning.
As the child grows, it becomes more important to that the parent have a grasp on the "knowledge" part of teaching or the child may become frustrated. If the parents skills are lacking, the child will suffer. The proverbial Master/Pupil theory of education becomes very important at this stage of the game. That is one reason we encouraged our oldest kids to start taking classes at the local Junior College when they were 15 or 16. They were beyond our abilities to teach "knowledge" in some subjects.
If I am not mistaken, education followed this pattern up until the mid-1800's. Parents taught the children the basics at home, and then the child, if he/she displayed above average abilities, might be privately tutored or sent to university for a formal education. Other children, with lesser abilities, were apprenticed into a family business or some local trade.
As to the idea that a child might develop to the point where s/he can develop further only with guidance from someone more expert than the parent, I would say that unless the parent is raising the child to follow directly in his/her own footsteps, that is a question not of "if" but of when.
And speaking of a child following in a parent's footsteps, here's a case for you:
dad runs contracting businessWhat will come of that boy? Just like an immigrant to America wants to go home a success or not at all, our emigrant from school to work had something to prove. The son takes over the father's business, increases its profits, and retires to Florida well-off. No college degree, nor even a high school diploma. Both his daughters are prosperous college grads--and he never broke a sweat paying for their tuition.son shows up on the job site
dad says, "Why aren't you in school?"
son says, "School is boring and I want to work."
dad says, "You'll never wear a white shirt."
son says, "I know."