Old thread, but I found it doing a google search trying to answer a similar question as the original poster.

Just found out, or understood, that in our system no one is a sensei until they are 3rd dan or higher.

2nd dan and lower are sempai.

In the same token, a brown belt can teach here - seems I read somewhere that stateside usually 2nd dans teach.

People here dont typically get their brown belt, from what I have seen, until 7 years or so.
Black is typically longer by the looks of it.

Anyway, it seems it really is a depends on system then.
I was under the impression that if you were black belt and teacher you were a sensei.

Peace

dAlen