[Nyororin]

Native speakers don`t have the inherent ability to teach their native language. A native speaker can be worse a teacher than a non-native speaker in many cases...

A trained native speaker will pretty much always top a trained non-native speaker. Unfortunately, when there is the choice between a skilled non-native teacher and an unskilled native speaker, people will choose the native just because, well, they`re native. I think this is probably the root of negative images of native "teachers" - in many cases, it is just assumed that if they speak it they can teach it.

If trained, it`s also going to depend on the person. Even with the exact same education, there are "good" teachers and "poor" teachers. Some people are just better at teaching than others.

I`m a native English speaker, and have taught English at various points in life.
Even with training, I suck at teaching conversation and avoid it at all costs.
However, I am apparently very good at teaching grammar and written English... Native English speakers who can teach for written (entrance) exams and the Eiken seem to be at quite a premium. If I wanted to go through the pain of getting a normal teaching license, I`m sure I would have no trouble being a regular English teacher in a Japanese school.

I only wish I were as good at teaching Japanese - for some reason I find it incredibly easy to explain English grammar in detail, with comparison examples in Japanese... But am nowhere near as smooth going the other way. It seems that as I mainly do Japanese to English translation, I should have less trouble explaining extremely familiar points of Japanese in English. The opposite is true. It`s a bit of a mystery.