"He doesn't understand how anyone can not understand."
My daughter and I were discussing why somebody would make a lousy teacher, and this was her observation. I realized that I have seen student teachers with this problem-- they do not understand how anybody can NOT understand the concept at hand, and so they have no idea how to teach it.
This is a smart person's problem. Some smart people never learn to be reflective, and they never look at their own process. Or they do look at their process, and to them, the process of building understanding goes kind of like this:
1) Look at something
2) Understand it
This leads to lousy teaching, the kind of teaching where a math teacher puts a problem on the board and a student asks a question about how to solve it and the teacher just says (with no small amount of exasperation), "Well, just look at it!" As any student who has ever been on the receiving end of this approach can tell you, this is not super-effective pedagogy.
The effects of this attitude are worse than simple bad teaching. Because if I believe that all learning requires is to just look at the stuff and just, you know, try to understand, and I have students who say they don't understand (and prove it on assessments), then I can only reach one conclusion-- the little buggers just aren't trying. I begin to resent them for withholding work and achievement (they could do it if they wanted to). I snap at them for asking questions, because they only ask questions because they are too lazy to understand. Some of them have stories about obstacles, like not having homework done because their father threw them out of the house last night. This is just excuse making, like the whole "I don't understand" thing. If they really wanted to try, they could tough it out (because we all know that it's not really that hard to understand stuff).
Sadly, most of us probably know at least one teacher like this, but even more sadly, we can recognize this complex of attitudes from some of the Reformsters. It's the whole attitude that schools are failing because students and teachers just aren't trying. Try, dammit. Try harder.
We've been asking for years now how such smart people can come up with so many dumb ideas about fixing schools, but I would submit that they come up with these dumb ideas precisely because they are smart people-- smart people who have no idea what it's like to not understand something.
In some cases, they don't even remember what it was ever like to not know certain things. The funny gaps in some CCSS materials might be there because smart people figure everybody "just knows" that. Directly teach six-year-olds how to set up addition of three-digit numbers? Not necessary-- they can just figure it out. Everybody just knows how you do that.
There is noise periodically about how not enough teachers come from the top percentages of college classes, and it may or may not be true, but why do we care-- do we not all remember the teacher who was really, really smart, but a terrible teacher because he couldn't explain anything?
Now, smart people can also be excellent teachers. One of their best tricks is to be able to see multiple paths to understanding, a hundred different sets of tracks to follow through the forest of confusion. And it is a great teaching gift to be able to see where exactly in those not-so-lovely but oh-so-dark-and-deep woods the student is lost. There's no reason that such gifts can't go hand in hand with smartness.
But people who do not understand what it's like not to understand, people who think you just try and you know, people who believe the only way to fail a test is to be too lazy and shiftless to have tried-- these people may be smart, but they make lousy teachers. They make even lousier education policy.