I remember both the kind ones and the ones who thought they were Genghis Khan. I have to say that one was not more effective than the other. In fact, the little dictators were probably the least effective teachers. In my experience, students spent time hating the teacher instead of learning.
The teachers who were firm without cruelty were the best. Those were the ones who usually expected a lot from the students. In other words, they pushed you to live up to your potential. And you respected them as well. Treat people as humans and they will respect you in return. It's a simple as that.
That's interesting. My favorite teacher was the teacher of math as well and she would tell us the same thing. Moreover, sometimes we'd study until midnight after exams having been fixing our mistakes. She was a kind of human who had nothing but her math. No family. No children.
I respect her until now and will do forever.