I started teaching guitar in classes only and then a private lesson practice started to grow from that. Now it is about half in private, half in classes. The private lessons were charged per lesson; but I began to have that problem of people canceling at the last minute and then I would not get paid. So, I instituted a monthly tuition with a contract and with the stipulations for how to re-schedule a canceled lesson.
However, there is a problem. About 8-9 times a year there is that extra lesson in the month, due to a longer month. My students meet with me every other week or (what is usually) twice a month. Sometimes it works out that it is 3 times a month. When they were paying per lesson, the parents didn't notice this -- as it was every other week. Now they are noticing it and it is becoming a very uncomfortable issue for me to ask that they pay for 3 lessons rather than 2 as it's a long month. Because lessons are one hour it "looks" like a LOT more money to them and some of them have made uncomfortable remarks to me.
How do the rest of you handle this situation?