If you have to cancel a lesson, I operate the following policy:
Planned absence (eg, holiday, school trip, appointment, date, anniversary, whatever) – 1 week’s notice is required or the lesson must be paid for.
Unplanned absence (eg. illness, car problems, etc.) – written notice (text or email) is required by 9am on the day of the lesson or the lesson must be paid for.
Emergency absence (broken leg, car crash on the way to lesson, family emergency etc.) – let me know, I’m a nice guy, we can probably sort something out…