Some have wrongly thought that if they know a subject matter then they can teach it. Some have claimed the title teacher, mentor, professor or what-have-you just because they know a great deal in a field of study. It takes more than knowledge to become a teacher, a lot more to become a good one, and a whole lot more to be great.

Being good at Math doesn’t make one a Math teacher. Having a perfect accent and impeccable grammar doesn’t make a person an English teacher. And if by luck, accident, mistake or necessity, a person was given a teaching load by virtue of just being good at a particular field then that’s very unfortunate, a disservice to the teaching profession.

There’s a whale of difference between knowing a subject matter and knowing how to teach it. It is not a guarantee that when one is an expert in a domain of knowledge that he could be a  teacher in that field. Perhaps he has the potential to become one for he already possesses one of the requirements to become a teacher…and that is mastery in a discipline. But expertise in a field, knowing what to teach, is just the beginning of the journey we call teaching.

Source: What Makes A Great Teacher