Larry Moran thinks I have the wrong idea about teaching evaluations and “thin slicing”:

Unfortunately, Dave Munger seems to draw the wrong conclusions from this study as he explains in an earlier posting [The six-second teacher evaluation]. In that article from last May he says …

So we do appear to be quite effective at making judgements about teaching ability even after viewing only a total of 6 seconds of actual teaching, and without even hearing the teacher’s voice.

This is dead wrong. Students are good at evaluating something after six seconds but it sure as heck ain’t teaching ability.

If you’d like, you can check out my (and PZ Myers’) responses over there, but I did want to add a few words here. First of all, in a way, Moran is right. Student evaluations of teachers are not the only way of measuring teacher performance, and they very likely aren’t the best way. However, if you read my entire post from last May, you’ll see that wasn’t my point.

In the Ambady and Rosenthal study, teachers weren’t just being evaluated by students. Principals also evaluated the teachers, and those ratings correlated with the 30- and 6- second “thin slices.” Also, the “30-second evaluation” is a bit of a misnomer, because the 30 seconds were actually 10-second snippets taken from three different parts of a class. That’s a whole lot more information than just a single 30-second snippet, because teachers were probably doing different things in each 10-second snip. This is what correlated significantly with end-of-course and principal’s evaluations of teacher performance.

Also, there’s a bit of verbal maneuvering (perhaps unintentional) in Moran’s post. I say we can make “judgements” about teaching ability in 6 seconds, but he changes that to “students are good at evaluating,” which implies a higher level of analysis. In fact, I reported that along certain dimensions of teaching ability, the judgements that can be made in 30 seconds are correlated with end-of-semester judgements: dimensions such as “confidence” and “optimism” correlate at an impressive level of r=.82 and .84 respectively. But when we evaluate a teacher, we’re doing much more than offering an impression of his or her character; we’re assessing how well he or she can help students learn. Obviously confidence and optimism are good traits for a teacher to have — and it’s impressive that our 6-second judgements about of these traits aren’t much different from 6-month judgements, but in the end, that isn’t what we mean when we’re talking about a good teacher.

My take-home message from the post I wrote last May was simply this: that end-of-semester student evaluations aren’t much better than initial impressions, so if you’re a student trying to decide whether to take a class, you might as well just visit on the first day; it’s just as effective as poring over those guidebooks of the student evaluations that are distributed on many college campuses. (Even more important: are you interested in the content of the class — you’ll spend more time studying on your own than you will in class!)

The point of the “Blink” methods now being applied in the classroom post was to show how results like Ambady and Rosenthal’s are, well, being applied. At least in the case of the Charlotte-Mecklenburg schools, it’s not true that teacher evaluations are being placed in the hands of students; rather, principals are using thin-slicing to evaluate a larger number of classes than was previously possible. I’d certainly rate this as an improvement over the system that was in place during my brief tenure as a teacher, which is that the principal didn’t visit classes at all.

But if you find yourself agreeing with Moran, or if you think I’m misrepresenting him — or myself — please let me know in the comments.