A good teacher?
1. Ability to communicate - clearly, firmly (with kids) and tactfully (what to say but more importantly, what not to say). Encouraging in effect.
2. Endless patience.
3. Creative - can use different approaches/methods/strategies if one or the other does not seem to be working.
A sense of humour and an ability to inspire would be added bonuses!

A poor teacher would be the opposite, I guess...
PS.
My daughter has an absolutely wonderful teacher and I'm trying to work out how else he could be better or what weakness he may have but I'm having a splitting headache and a slight fever right now, so, this will have to wait till I'm better.

Good night.