Gladwell makes two major points: (1) for some occupations, you can't tell how good someone is going to be until he or she is actually practicing that occupation; and (2) good teachers have a quality that he calls (after Jacob Kounin) "withitness" and that I've always thought of as watchfulness. What this means is that a good teacher is always aware, as far as possible, of what's going on in the class--not just the activities, but the level of engagement.
It's easy to tell if students are engaged in a class if they're talking, but what if they aren't? Someone once commented after watching me teach, "you watch faces." I don't know if that's good or bad, but watching faces enables me to see if people are paying attention before they completely check out. Of course, no one can do this all the time; if that were true, Planner Girl wouldn't have gotten as far as she did with checking out of the discussion because I'd have noticed it earlier.
I've observed a lot of people's classes over the years, and "withitness," the ability to relate to individual students while keeping the group together as a whole, really stands out as something that keeps students engaged and motivated. Gladwell gives this example:
Then there was the superstar—a young high-school math teacher, in jeans and a green polo shirt. “So let’s see,” he began, standing up at the blackboard. “Special right triangles. We’re going to do practice with this, just throwing out ideas.” He drew two triangles. “Label the length of the side, if you can. If you can’t, we’ll all do it.” He was talking and moving quickly, which Pianta said might be interpreted as a bad thing, because this was trigonometry. It wasn’t easy material. But his energy seemed to infect the class. And all the time he offered the promise of help. If you can’t, we’ll all do it. In a corner of the room was a student named Ben, who’d evidently missed a few classes. “See what you can remember, Ben,” the teacher said. Ben was lost. The teacher quickly went to his side: “I’m going to give you a way to get to it.” He made a quick suggestion: “How about that?” Ben went back to work. The teacher slipped over to the student next to Ben, and glanced at her work. “That’s all right!” He went to a third student, then a fourth. Two and a half minutes into the lesson—the length of time it took that subpar teacher to turn on the computer—he had already laid out the problem, checked in with nearly every student in the class, and was back at the blackboard, to take the lesson a step further.
That's why, I think, teaching takes so much energy and we all talk about how tired we are at the beginning of the semester. If teaching doesn't take a lot out of you, in the immortal words of LOLcats, "Ur doin it wrong."