No shows
We were having a lot of trouble with no-shows for a while. It's very hard to charge a no-show fee to someone who isn't there! Solution is they now have to pay a deposit when they make a booking, and they get a text to remind them about thier lesson the day before. If they don't show, the deposit is lost, (half is lost for a late cancellation) and it doubles for their next booking. If they chose not to pay a deposit then they can be booted if someone else wants the slot, and they pay a higher hourly rate.
It doesn't cover the losses but it has made a huge difference in preventing no-shows and late cancellations.
Back on subject, what my part timers earn is largely up to them, I provide the infrastructure, they can then develop their career within it as much or as little as suits them, but they know I don't "owe" them a living.