The LA Times investigative report on teacher quality is groundbreaking. The teacher’s union has already started a boycott but, as the shock recedes, I think this is going to be emulated throughout the country. It should have been done decades ago.

The 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 L.A. teachers – something the district could do but has not.

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….

In coming months, The Times will publish a series of articles and a database analyzing individual teachers’ effectiveness in the nation’s second-largest school district – the first time, experts say, such information has been made public anywhere in the country.

Not much data is available yet but what is astounding is that the LA Times will release information on individual teachers. The graphic below, for example, is not an illustration it is real information on the real teachers named. To understand the importance of these differences note that:

After a single year with teachers who ranked in the top 10% in effectiveness, students scored an average of 17 percentile points higher in English and 25 points higher in math than students whose teachers ranked in the bottom 10%. Students often backslid significantly in the classrooms of ineffective teachers, and thousands of students in the study had two or more ineffective teachers in a row.

With better information there is a possibility that teachers will improve. Simply knowing that other teachers do better will encourage the lower performing teachers to ask why and to emulate best practices.

Unfortunately, we have little idea how to train good teachers. The best we may be able to do is to throw a bunch of people into the classroom and measure what happens but for that strategy to work it needs to be followed up with firings. Indeed, one recent study (see here for another explanation) found that the optimal system–given our current knowledge and the importance of teacher effects–is to hire a lot of teachers on probation and then fire 80% after two years, yes 80%.

I don’t blame the unions for being up in arms and I feel for the teachers, for some of them this is going to be a shock and an embarrassment. We cannot simultaneously claim, however, that teachers are vitally important for the future of our children and also that their effectiveness should not be measured.  As systems like this become more common students will benefit enormously and so will teachers.

Moreover, I see this as a turning point. Once parents have this kind of information who will allow their child to be in a class with a teacher in the bottom ranks of effectiveness? And if LA can do it why not Chicago and Fairfax?

Many people said that information technology would revolutionize teaching but few had this in mind.

Addendum: Details on methods here.