Inkwell has already praised the Los Angeles Times (will miracles never cease?) for its excellent series on teachers in the L.A. public school system. The paper stirred up controversy-including a threatened newspaper boycott by the union!-by publishing grades of teachers.

The system of grading is known as value-added-using standardized tests, the method tries to assess the difference the teacher made to a student over the course of a year. No doubt, this can in some instances be unfair. But, with our school system in disarray, we do need some tool for measuring the quality of teaching.  Writing in City Journal, Marcus Winters agrees with Inkwell that the L.A. Times performed a great public service:

The Times has admirably highlighted the importance of using data to evaluate teacher performance, confirming the findings of a wide and growing body of research. Studies show that the difference between a student’s being assigned to a good or bad teacher can mean as much as a grade level’s worth of learning over the course of a school year.

While parents probably don’t need studies to tell them who the best teachers are-such information is an open secret in most public schools-academic research helps underscore the inadequacy of the methods currently used to evaluate teacher performance. Even the nation’s lowest-performing school districts routinely rate more than 95 percent of their teachers as satisfactory or higher.

That last factoid points to why the L.A. Times story was so controversial: protected by unions, teachers are rarely subjected to the kinds of professional judgments others face. They are virtually fireproof in many school systems.

Winters goes on:

Teacher evaluations yield absurdly positive results because they’re not tied to objective measures of performance. The current system relies on classroom observation, a thoroughly subjective measure. Tenure protections ensure that poorly rated teachers can’t be removed even when they receive poor performance reports. The result? Principals everywhere hand out positive evaluations to undeserving teachers.

There are reasons to worry about over reliance on test scores in evaluating teachers. If it weren’t for the unions, some subjectivity would not be worrisome. There are also many factors beyond a teacher’s control-think of the kid who comes to school after a scene of domestic violence or who is growing up in the poverty of a single-parent household. How much difference can one teacher make?

But let Winter have the last word:

The Times analysis makes clear that many of L.A.’s teachers just don’t belong in the classroom. That’s an important service and represents journalism at its best. However, the paper’s promise to create a public database linking individual teachers by name to their measured influence on student proficiency-a move lauded by Duncan and reportedly being considered by Washington, D.C., school chief Michelle Rhee-is worrisome. Publicly listing each teacher’s value-added scores would imply that test-score analysis is sufficient.