I Disagree
A lesson is a service, if you agree on a price for 1 hour of lessons, did the instructor stop at exactly 60 minutes??
Probably not he completed the segment he was working on with you, and maybe even some more.. This is a service that they provide not like buying a lesson at Wal Mart!
I have a tendency to tip for services provided, hell one of the rooms I frequent has free pool on Mondays and Fridays from 4 to 8 pm, I tiup out the guy behind the counter with a $fiver, just for his time, the results in return will far outweigh the meager few dollars....
I feel any person in the sevice or instruction industry almost always goes beyond what they had agreed on at the onset, and should be compensated for that extra service he/she provides..
Joe