Editor’s Note — This article has been corrected from a previous version. The LA Times did not hire the RAND Corp. to conduct this analysis, but was assisted by a RAND Corp. researcher.

LOS ANGELES — The Los Angeles Times is publishing an independent analysis of the best and worst teachers in the Los Angeles Unified School District using a "value-added" approach that shows wide variation in teacher effectiveness, it reported. The city teachers union is launching a boycott of the newspaper in response, the Times reported.

Aided by a RAND Corporation researcher, the newspaper conducted a statistical analysis of student scores on standardized tests in math and English over seven years.

It grouped the results by teacher and found that students of some teachers consistently made larger gains in a single year than those in other classrooms, and more than would be expected based on the students' past scores, the report said. Conversely, it found that students of other teachers consistently lost ground, the Times reported.

The difference could not be attributed to class size, socioeconomics or parental support, the Times reported. The Times said it will publish the entire database later this month, after first inviting teachers to view it and post comments.

The district could have done the same analysis but has not, the Times reported.

Critics of value-added models say that standardized tests are flawed, and that they do not capture intangible benefits of a given classroom, the Times reported. Supporters say it is the best method to date of objectively evaluating teacher performance.

Los Angeles Times, "Who's teaching L.A.'s kids?" Aug. 14, 2010

Los Angeles Times, "Union leader calls on L.A. teachers to boycott Times," Aug. 15, 2010

Mackinac Center for Public Policy, "Using Value-Added Assessment to Define Teacher Quality," June 30, 2008