"But we DO see scores of unfilled teaching positions. "
Where?
This should answer your question. Is your head really that far in the sand that you're unaware that there's a teacher shortage in this country?
http://www.ed.gov/about/offices/list/ope/pol/tsa.pdf
"The normal capitalistic forces don't work with teaching"
Yes, they do, and they are working. The decisions are made by organized labor, intent on the maximum amount they can "harvest" from a school district. The winning play for them is low/no teaching standards, tenure as a proxy for ability, and the resulting low wages due to oversupply.
The unions will tell you it's dollars and class size, the data will tell you those have very low correlation with outcome.
Socialism's last hope in America is our public school system.
It's a difficult situation, and there are a number of factors on both sides of the issue that complicate things. The system does need reform, but changes need to be made in a way that keeps both sides happy.
If you just raise qualifications for teachers without anything in return, you just drive more qualified people away.
Something like raising qualifications needs to happen in tandem with better compensation. If your boss suddenly said you needed to fork out for more education but you would get nothing in return, would you do it or would you go work somewhere else?
Tenure exists because it's the only way schools have been able to attract teachers to a job with so many other downsides. Getting rid of tenure with no other changes would just drive qualified people away from teaching. Personally, I think it would be good to get rid of tenure but only in tandem with other changes to compensate, and better attract qualified people to the teaching profession.
Teachers aren't in a position to demand more money (other than striking, those evil pinko commie unions). If the teaching profession doesn't pay well and provide incentives competitive with other jobs, the best and the brightest will go to those other jobs.
To simply make a blanket statement that pay is adequate is simply moronic.
In any other business, if you were offering minimum wage and not getting qualified applicants (and you would get applicants, just not quality ones), do you honestly think that raising qualifications would get better people to apply? You offer a better salary, and THEN when you get more applicants to choose from.
With no incentive for qualified workers, your options are to leave the jobs unfilled or lower standards. How can you say "it is working" when the american educational system is so bad right now?