I'm in a cover band with a teacher, i havent had him for classes since year 9. He was the Duke of Edinburgh teacher, so everyone gets to know him really well through that. But he's the kind of person that is easy to get along with.
my music teacher and i were more like friends than teacher/student, coz we had a tiny class in yr12, she's only in her mid-20s or so (she won't tell us exactly )... she wouldn't find it weird at all if i just called her up for a chat or something lol.