From today's WSJ:
New York City on Friday released for the first time a database ranking nearly 18,000 public schoolteachers based on their students' test scores, a historic move that lifted the curtain on one measure of quality in the classroom.
How can it be that teachers are only now being evaluated on the basis of their work output? A teacher's job is to instill knowledge of a subject in their pupils. It seems only rational that their performance would be judged on the basis of how much knowledge they instill. By what standard have they been measured up to this point?
Of course, the answer is that they haven't been held to any standards whatsoever. That fact is reflected by the teachers' and union's zealous opposition to the evaluation database. The unions have a lucrative public monopoly over education and teachers are immune from discipline based on their performance - neither group have an interest in subjecting themselves to criticism, implementing objective standards of performance and upsetting the status quo.
I've written on American educational exceptionalism before and have been heavily critical of unions and public school unaccountability. The education bureaucracy surely sees any form of comparable evaluation criteria as one step in the direction of market competition in American education. Competition would certainly favor private, parochial schools - to the fiscal and political detriment of unions and to the utter dismay of liberal secularists. These cultural, political and economic factors are the true motivations behind America's public education policies and the opposition witnessed to teacher evaluation databases.