How are we going to prevent children being taught by "unqualified" teachers?

First of all, to know what is meant by "qualified", we have to know what is meant by quality.  We could hardly agree on who was or was not a good painter if we did not to a large extent agree on what was or was not a good painting.  The question asked above assumes that since educators agree on and understand correctly what is meant by good teaching, they are able to make sound judgments about who is or is not a good teacher.  But the fact is that educators do not understand or agree about what makes good teaching.  The dismal record of the schools is proof enough of this.  This further proof is that, when charged in court with negligence, educators defend themselves by saying (with the approval of the courts) that they cannot be judged guilty of not having done what should have been done, because no one knows what should have been done.  This may be so.  But it clearly follows that people who don't know what should be done can hardly judge who is or is not compentent to do it. 

In practice, educators who worry about "unqualified" people teaching their own children almost always define "qualified" to mean teachers trained in schools of education and holding teaching certificates.  They assume that to teach children involves a host of mysterious skills that can be learned only in schools of education and that are in fact taught there; that people who have this training teach much better than those who do not; and indeed that people who have not had this training are not compentent to teach at all.             None of these assumptions are true.

Human beings have been sharing information and skills, and passing along to their children whatever they knew, for about a million years now.  Along the way they have built some very complicated and highly skilled societies.  During all those years there were very few teachers in the sense of people whose only work was teaching others what they knew.  And until very recently there were no people at all who were trained in teaching, as such.  People always understood, sensibly enough, that before you could teach something you had to know it yourself.  But only very recently did human beings get the extraordinary notion that in order to be able to teach what you knew you had to spend years being taught how to teach. 

....And in fact these are not what schools of education talk about.  They give very little thought to the act of teaching itself--helping another person find something out, or answering that person's questions.  What they spend most of their time doing is preparing their students to work in the strange world of schools-which, in all fairness, is what the students want to find out: how to get a teaching job and keep it.