New York City will release value-added rankings of teachers in fourth through eighth grade, if a United Federation of Teachers lawsuit fails. That’s intensified the debate over evaluating teachers based on their students’ progress, reports Education Week.  Traditionally, virtually all teachers — from Mr. Chips to Mrs. Burnout — are judged “satisfactory.”

“It’s universally acknowledged—teacher evaluations are broken,” said Timothy Daly, president of The New Teacher Project, a group that helps school districts recruit and train teachers.

Perhaps surprisingly, teacher-union leaders agree. Michael Mulgrew, president of New York City’s United Federation of Teachers (UFT), said last spring that “the current evaluation system doesn’t work for teachers—it’s too subjective, lacks specific criteria and is too dependent on the whims and prejudices of principals.”

Mulgrew supported New York’s new evaluation system, which counts student achievement as 40 percent of a teacher’s rating.

“Value-added” measurements use complex statistical models to project a student’s future gains based on his or her past performance, taking into account how similar students perform. The idea is that good teachers add value by helping students progress further than expected, and bad teachers subtract value by slowing their students down.

Value-added modeling is too inaccurate to be used as the “primary way to evaluate teachers,” says an Economic Policy Institute statement signed by many prominent education researchers. In addition, “an excessive focus on basic math and reading scores can lead to narrowing and over-simplifying the curriculum to only the subjects and formats that are tested, reducing the attention to science, history, the arts, civics, and foreign language, as well as to writing, research, and more complex problem solving tasks.”

Although standardized test scores of students are one piece of information for school leaders to use to make judgments about teacher effectiveness, such scores should be only a part of an overall comprehensive evaluation.

Diane Ravitch, one of the signers, argues against releasing teacher performance data in the New York Daily News.

Twenty-five states and hundreds of districts use measures of student achievement in teacher evaluations, writes Richard Colvin on HechingerEd. However, student achievement counts for less than half of a New York  teacher’s evaluation. So, it’s not the primary way teachers are evaluated.

I don’t think anyone argues that value-added scores should be the primary way to evaluate teachers. The question is whether the scores, which will be available only for some teachers, should be used at all.

My problem is that the other aspects of “comprehensive evaluation,” such as classroom observations, are subjective and “dependent on the whims and prejudices of principals.”  Many teachers say they have no faith in their principal’s ability to judge good teaching fairly and intelligently. If teachers’ effectiveness can’t be judged accurately by principals and can’t be judged accurately by student achievement, what’s left?

Update: Ed Sector’s Bill Tucker looks at how New York City is Putting Data Into Practice “to create an evidence-based and collaborative teaching culture.”