Jim Manzi has some smart things to say about teacher evaluations

From the National Review (via Chait, but more on that later)

This seems like a broadly sensible idea as far as it goes, but consider that the real formula for calculating such a score in a typical teacher value-added evaluation system is not “Average math + reading score at end of year – average math reading score at beginning of year,” but rather a very involved regression equation. What this reflects is real complexity, which has a number of sources. First, at the most basic level, teaching is an inherently complex activity. Second, differences between students are not unvarying across time and subject matter. How do we know that Johnny, who was 20 percent better at learning math than Betty in 3rd grade is not relatively more or less advantaged in learning reading in fourth grade? Third, an individual person-year of classroom education is executed as part of a collective enterprise with shared contributions. Teacher X had special needs assistant 1 work with her class, and teacher Y had special needs assistant 2 working with his class — how do we disentangle the effects of the teacher versus the special ed assistant? Fourth, teaching has effects that continue beyond that school year. For example, how do we know if teacher X got a great gain in scores for students in third grade by using techniques that made them less prepared for fourth grade, or vice versa for teacher Y? The argument behind complicated evaluation scoring systems is that they untangle this complexity sufficiently to measure teacher performance with imperfect but tolerable accuracy.

Any successful company that I have ever seen employs some kind of a serious system for evaluating and rewarding / punishing employee performance. But if we think of teaching in these terms — as a job like many others, rather than some sui generis activity — then I think that the hopes put forward for such a system by its advocates are somewhat overblown.

There are some job categories that have a set of characteristics that lend themselves to these kinds of quantitative “value added” evaluations. Typically, they have hundreds or thousands of employees in a common job classification operating in separated local environments without moment-to-moment supervision; the differences in these environments make simple output comparisons unfair; the job is reasonably complex; and, often the performance of any one person will have some indirect, but material, influence on the performance of others over time. Think of trying to manage an industrial sales force of 2,000 salespeople, or the store managers for a chain of 1,000 retail outlets. There is a natural tendency in such situations for analytical headquarters types to say “Look, we need some way to measure performance in each store / territory / office, so let’s build a model that adjusts for inherent differences, and then do evaluations on these adjusted scores.”

I’ve seen a number of such analytically-driven evaluation efforts up close. They usually fail. By far the most common result that I have seen is that operational managers muscle through use of this tool in the first year of evaluations, and then give up on it by year two in the face of open revolt by the evaluated employees. This revolt is based partially on veiled self-interest (no matter what they say in response to surveys, most people resist being held objectively accountable for results), but is also partially based on the inability of the system designers to meet the legitimate challenges raised by the employees.

I found the point about techniques that hurt futures performance particularly good. When I was teaching, how well a class would go was greatly influenced by how well previous teachers had done their jobs. Did the students understand the foundations? Did they have a good attitude to the material? Good work habits and study strategies?

Teachers want reliable evaluations not just because they want to be rewarded for good work but also because they want to see incompetent teachers identified so that those teachers can be encouraged to do better, given training to improve their performance or, should the first two fail, fired. What they object to is having their fates rest on a glorified roll of the dice.