It never occurred to me to tip a ski instructor but I've read in a few forums online that maybe you are supposed to 
Would this apply to just private instructors (every time, or at the end of a few private lessons?), or should it also be for group lessons or your child's teacher in a group lesson, say? What sort of amounts are we talking here?
Please tell me you're not supposed to tip instructors at ski slopes over here too 
What do other people do?
Also, are there other people you're supposed to tip (on a ski holiday, obviously!) and how much? I left some money for the chalet hosts at a chalet I stayed in a few months ago but I had no idea if I'd insulted or delighted them with the amount!