http://www.newyorker.com/reporting/2009/08/31/090831fa_fact_brill
Outstanding NewYorker article "The battle over New York's worst teachers".
Please do not think of this as an article about the teaching profesion. Think of this nonsense relative to unions for all government employees (like all those new health workers we are about to get) and how unions mock common sense.
Teaching (like manufacturing cars or brain surgery) can ge done poorly or with excellence. The important question is how does a union environment impact the quality and cost of the service delivered?
In the private sector (the auto industry not withstanding) when managment commits to a dumb contract the company usually goes out of business and the contract becomes a non-issue. But when a government monopoly (like education or air traffic control) signs a dumb contract there are few mechanisms for correcting the mistake and years later the public is still suffering. After all the government monopoly makes it virtually impossible for new entrants to compete.
This is possibly the strongest argument for having government doing less for us rather than more. We all make mistakes but government is incapable of correcting these mistakes.