Two weeks' notice seems to be the thing, although in the case of a teacher in the middle of the school year you will be leaving both the school and the students in the lurch. You may want to consider longer notice for those reasons.
Be aware though that your giving two weeks' notice does not stop them from saying, that's ok, get out today. Be prepared for that. I know people who gave two weeks' notice and immediately got the bum's rush,