The city teachers union today formally asked the comptroller and special commissioner of investigation to examine the accuracy of the Department of Education’s teacher ratings.

The move comes after an ongoing back-and-forth between the union and the city over how city officials ensure the accuracy of the data that determine the ratings. Yesterday, the union called a press conference to share stories of teachers who discovered that their data reports rate their effectiveness based on students and subjects they had never taught.

The feud over the ratings began in October, when city officials announced that they intended to release the teacher rankings to reporters. Union officials began collecting examples of errors on the reports, and then sued to block the release, arguing that the reports were too riddled with inaccurate information to be released.

Teachers union President Michael Mulgrew said Sunday that his staff has documented at least 200 cases in which teachers’ reports include errors. In its court filings, the union gave nearly 20 examples of reports, with teachers’ names redacted, that the union claims reflect errors.

But city officials countered today in a letter to Mulgrew that because there were no names attached to the examples the union cited, they have been unable to verify the letters. The letter, signed by Deputy Chancellors Shael Polakow-Suransky and John White, asked the union to share the details of those cases.

Mulgrew responded by formally asking City Comptroller John Liu and Special Commissioner of Investigation Richard Condon to audit how the reports were created. “Because the DOE has already received the information requested in your December 20, 2010 letter and refused to take action, the United Federation of Teachers was compelled to” request the audit, Mulgrew writes.

City officials have said that the classroom-level data used to calculate the ratings was both provided and vetted by principals. But teachers speaking on Sunday reported that their principals were also concerned by mistakes in the reports but had been unable to correct the reports.

Cara Cibener, a humanities teacher at Tompkins Square Middle School, said her report was based in part on the test scores of students she never taught, and showed their progress on their exams in a different subject than the ones she taught.

“To be rated as an above average math teacher, when I’ve never taught math, and a below average [English Language Arts] teacher…is hard to see,” she said. “It doesn’t help me as an educator; it doesn’t help me serve my students better; I don’t think it would be enlightening for anyone outside of the school system to see.”

Cibener said she agreed with the city that parents should know what is happening in the classroom, but argued that releasing flawed ratings would cause parents to draw unfair conclusions before they get to know a teacher.

“Most teachers would be happy to talk to parents,” Cibener said. “It would be a shame if this ended the conversation.”

Robert Freeman, executive director of the state’s Committee on Open Government, said that as far as the laws on releasing the records are concerned, it doesn’t matter whether the reports are based on accurate data or not.

“If a record says that 2 and 2 equals 5, and there’s no exception that applies to that record, then it can be released,” Freeman said. “[The freedom of information law] does not deal with the accuracy of the record.”

Here is the letter Polakow-Suransky and White sent to the union this afternoon:

And here is the union’s response: