I have an 11 year old and he starts middle school this year. I have also taught in the public school system for a year. I've given this a lot of thought, and this could be a long post.

First of all, the United States has committed its public schools to give everyone, regardless of ability a free education. It has to be taken into account when comparisons are made between public schools and private schools that variables must be isolated before any legitimate conclusions may be drawn.

What are the variables?

Public schools must support a large transportation infrastructure while private schools do not.
Public schools must accept every kind of student in the jurisdiction, and even provide home bound education to those unable to come to school.
Public schools must employ state certified teachers. A Bachelor's alone is not acceptable.
Public schools must pay teachers more because of the unions and lack of competition (certification drives down competition).
Public schools must retain undesirable teachers due to tenure.
Public schools must meet all federal and state guidelines.
I'm sure there are others.

Right away some questions arise.
Why is the public still paying for transportation?

Why isn't Einstein qualified to teach physics in Tennessee?

What is the validity of teacher certification?

Why aren't we using merit based systems to promote good teachers?

How do we measure good teaching?

Why are teachers paid the same based on years experience?

Why do teachers get raises as a group instead of as individuals?

I will have to say that my 11 year old being bipolar, I'm not welcome at the private schools. So, at least for now, I think there is a need for public schools. (For me there is!)

But all this teacher stuff drives me nuts. I believe that good teachers are the key to good education. Billy Beane believes that good baseball players are the key to a good baseball team. (Moneyball) From Moneyball I get two things: it's vitally important to have valid measures of success, and the market rewards entities who can find and utilize undervalued assets.

From my post you can tell that I'm not real sure as yet how to positively identify the best teachers. But let's assume that some teachers are better than others, and that most students, parents, teachers, and administration have a good idea who they are.  Why can't my school hire them away from other schools? No incentive.

I will voluntarily eschew tenure and the union in return for incentive based pay. I am a great teacher, and feel confident that I can out work, out teach, and out perform 90% of the teachers out there. My students love me. Their parents love me, and when I'm done with them, the students are rewarded with skills that have earned them as much as $45 an hour.

Take a look at my shameless self-promotion, I mean uh, resume:
http://www.pronetric.com

And Moneyball:
http://en.wikipedia.org/wiki/Moneyball

It was really good book. It was written as a narrative with stories and biographies that come together to create the excitement of Harry Potter novel. (That was hyperbole.)
-dave