In article , " wrote:
[...]
There is no magic to teaching. ...well, other than having a
good grasp of the subject matter [...]

Absolutely untrue. That is only half the battle.

Two things are required in order to be able to teach:
1) Adequate knowledge of the subject matter
2) The ability to communicate that knowledge effectively

The latter category includes being able, when necessary, to explain the
concept in more than one way. When students experience difficulty grasping a
new concept, they often find it difficult to express exactly what it is that
they don't understand, or why they don't understand it. The best teachers are
those who can see where the students are having difficulty, and guide them
past the trouble spots. All this is part of communicating knowledge
effectively -- if I explain a concept in terms that are perfectly clear to
*me* but unclear to *you*, I have not communicated effectively. Moreover, if
the concept is unclear to you, you probably do not know *why*. It's up to me
to figure out why my explanation was unclear, and recast it in terms that will
be clear to you. If I cannot do this, my communication will continue to be
ineffective.

A person may be the leading expert in the universe on a particular subject,
but if he is unable to communicate that knowledge clearly to another person,
he *cannot* be an effective teacher.