New York City released evaluations of some 18,000 public schools teachers to news organizations that had requested the information on Friday, overcoming a legal challenge from the teachers union.

According to the New York Times, New York City education officials in August of 2010 prodded education reporters to seek the rankings by filing Freedom of Information Act requests. The United Federation of Teachers sued, arguing that the names should be kept confidential, but in August a Manhattan appeals court unanimously decided otherwise.

They concern information of a type that is of compelling interest to the public, namely, the proficiency of public employees in the performance of their job duties, the appellate judges wrote.

The evaluations encompass math and English teachers who taught fourth through eighth grade between 2007 and 2010. The rankings are based on what is known as a Value Added assessment that tries to account for student progress by examining gains in test scores while considering factors that include the socioeconomic background of students. 

Critics say that such assessments are too rigid and do not accurately gauge teacher performance. New York City Schools Chancellor Dennis Walcott said the reports contained very rich data but added as a caveat that they are not comprehensive, noting that it's old data and it's just one piece of information.

The United Federation of Teachers was more direct, taking out newspaper advertisements that say releasing the evaluations unfairly demonizes teachers. The full page ads, which ran in the Wall Street Journal, New York Post and New York Daily News, displayed the complex formula used to grade teachers.

The Department of Education should be ashamed of itself, United Federation of Teachers President Michael Mulgrew said to the Wall Street Journal. It has combined bad tests, a flawed formula and incorrect data to mislead tens of thousands of parents about their children's teachers.

Devising more effective ways to rate teachers has been central to the education reform agenda embraced by both the Obama administration and New York City mayor Michael Bloomberg. It has been a highly contentious topic, with New York and the union just last week resolving a dispute over new teacher evaluation systems that had endangered nearly $1 bil in federal aid.

New York City began compiling the rankings released on Friday as part of a pilot program launched four years ago, and Mulgrew accused the city of reversing a pledge to keep the data confidential.

Because this procedure is highly experimental, then-Chancellor Joel Klein promised when it began that the results would only be available to teachers and their supervisors, Mulgrew said in the newspaper advertisement. Then the Department of Education reneged on its pledge and has them released to the public.

The Los Angeles Times sparked controversy in 2010 when it released the names of some 6,000 elementary teachers alongside data on how their students had fared on tests.