This week's New York Times supplement  on teaching once again skipped community colleges completely, even though it found several pages to dedicate to professors' clothing.
That said, it had one article that actually brought up a worthwhile issue, if indirectly.
Student evaluations of professors are usually coded statistically, and that works pretty well for professors who are generally considered great, average, or awful. If someone scores multiple standard deviations below the mean in every category, there's a pretty good chance that something is going badly wrong. While it would be a mistake to base a personnel decision on a single data point, there's nothing wrong with using data to highlight where a second, closer look is warranted.
But the statistical system doesn't do as well with professors who aren't "generally considered" any one thing. Some professors evoke polarized responses among students: simply put, they're either loved or hated. In the numbers, loved and hated might average out to something like "nothing special," but that's misleading. These are where the dreaded judgment calls have to be made.
Any number of things can lead to polarized responses. I'll start with the hot-button one of a 'political agenda.' Yes, some professors are ham-fisted (or seem that way, depending on your background) in how they present material, and students object to that. But to me, 'political opinions' and 'teacherly craft' are separable. I've seen professors with strong beliefs structure their classes to foster a vigorous exchange of ideas, and win the respect (if not the agreement) of those who disagree. The key variable here isn't so much a strong set of opinions, but the ability to run a class in a professional and ethical way.
(Annoyingly, some students simply won't tolerate any challenge to their pre-existing beliefs. A student once accused me of advocating cannibalism when I assigned Swift's "A Modest Proposal" as a reading. It took some time to get him to acknowledge that there can be value in reading things with which you disagree.)
More commonly, though, sarcasm tends to be polarizing. Those who feel secure in their grasp of what's going on often find it refreshing; those who are struggling often find it arrogant. This tends to hold true regardless of politics. At PU, one of my math faculty was widely despised by students, despite what I observed to be a clear and accessible teaching style. Over time I figured out that it was his sarcasm – gentle by my standards, but there it was – that set them off. Since they were struggling in the class, they heard the occasional aside – rightly or wrongly – as insulting.
Personality conflicts can also play a role. I had a class at SLAC with a professor whom just about everybody liked; I couldn't stand him. Everybody else found him charismatic; I found him smug beyond belief. Strong personalities will probably elicit more of these responses than others; whether that's right or wrong I'll leave to the ethicists. And those frustrating issues of cultural fit can fall under this category, too, with varying degrees of fairness.
Offbeat subject matter or teaching methods can also elicit unpredictable responses. In my experience, in-class role play exercises tend to either soar or flop, with little in-between. I've found that some level of honesty when things flop can actually go a long way with students. They read honestly, correctly, as respect, and respond accordingly.
I'll admit to getting a little nervous when a polarizing professor blames negative responses on the students. There's often some truth in it, but there's also the basic fact that the students are who they are, and teaching the students we actually have is the job. You'll never reach everybody, and that's to be expected, but I'm much more sympathetic to the professor who says "I'm having trouble with x group, so I'm trying this new strategy" than with the one who says "x group just isn't fit to be here." There's also the inconvenient fact that other faculty have the exact same students, and somehow seem to get through. If 8 out of 9 members of a department seem to be doing fine, and the 9th isn't, and the 9th's explanation is that her students suck, I tend to be skeptical. Anything's possible, but the burden of proof in that case is pretty heavy.
Wise and worldly readers – what do you think makes a professor polarizing? Have you been one?