The Los Angeles Times obtained seven years of math and English test scores from the Los Angeles Unified School District and used the information to estimate the effectiveness of LA teachers — something the district never elected to do:
The Times used a statistical approach known as value-added analysis, which rates teachers based on their students’ progress on standardized tests from year to year. Each student’s performance is compared with his or her own in past years, which largely controls for outside influences often blamed for academic failure: poverty, prior learning and other factors.
[...]
Highly effective teachers routinely propel students from below grade level to advanced in a single year. There is a substantial gap at year’s end between students whose teachers were in the top 10% in effectiveness and the bottom 10%. The fortunate students ranked 17 percentile points higher in English and 25 points higher in math.Some students landed in the classrooms of the poorest-performing instructors year after year — a potentially devastating setback that the district could have avoided. Over the period analyzed, more than 8,000 students got such a math or English teacher at least twice in a row.
Contrary to popular belief, the best teachers were not concentrated in schools in the most affluent neighborhoods, nor were the weakest instructors bunched in poor areas. Rather, these teachers were scattered throughout the district. The quality of instruction typically varied far more within a school than between schools.
Although many parents fixate on picking the right school for their child, it matters far more which teacher the child gets. Teachers had three times as much influence on students’ academic development as the school they attend. Yet parents have no access to objective information about individual instructors, and they often have little say in which teacher their child gets.
Many of the factors commonly assumed to be important to teachers’ effectiveness were not. Although teachers are paid more for experience, education and training, none of this had much bearing on whether they improved their students’ performance.
Other studies of the district have found that students’ race, wealth, English proficiency or previous achievement level played little role in whether their teacher was effective.
Naturally, the LA teachers’ union president is calling for a boycott of the LA Times.
(Hat tip to Katherine Mangu-Ward of Reason.)