Elizabeth Green , in her book[1] claims that this whole debate regarding teacher evaluation, free markets VS teacher autonomy is wrong. The answer lies in better teacher training. [2] Is an interesting article about that, which shows what can be done and how does it work when you offer better teacher training.
[1]http://www.amazon.com/Building-Better-Teacher-Teaching-Every...
[2]http://www.nytimes.com/2010/03/07/magazine/07Teachers-t.html...