Expertise
I was not the only person to see this tweet and have the following thought...
One of my college education professors drilled this into me, and my last thirty-some years of teaching have only confirmed it-- half the secret of classroom management is to know what the hell you're talking about. The best leverage for classroom management is neither love nor fear-- it's respect. And the best way to garner respect is to be competent, to display expertise in the content area, to know what the hell you're talking about.
Yes, teaching is both a skill and an art and to do a good job, you have to know the skill and the art of teaching. But just as you can't have waves without water or air, you cannot have "teaching skills" without content knowledge-- and all the teaching skills in the world will not make up for lacking knowledge. You cannot make an awesome lesson about adding two plus two if you do not know that the result is four. You cannot lead your students through an illuminating and inspiring study of CURMUDGUCATION: Expertise: