David: Hi, I won't be able to make tonight's lesson.
Frank: OK. Shall we reschedule for this week?
David: I can't as I have other things planned.
David: Let's just make it next week- same time next Friday.
Frank: OK.
David: Can you please email me all the materials that we were going to cover tonight.
Frank: I'm not home ATM but when I come back I will email you some exercises and worksheets.
David: Great. Thanks!
Frank: The other thing is that I would prefer that in the future you let me know at least 24hours in advance if you intend to cancel.
David: I'll try but it is not always possible.
Frank: I understand that but in the grand scheme of things I do set this time aside in my schedule for you so it would be fair to let me know.
David: I understand.
Frank: Otherwise it is really difficult to schedule and plan my work time.
David: But you can always teach another student tonight.
Frank: I'm afraid that it doesn't work that way. I can't just ring people and ask them to reschedule just because you cancelled.
David: Why not?
Frank: Because it means that they will have to reschedule their plans.
Frank: And that would be really unfair.
David: I see what you mean. 
David cancels tonight's lesson with Frank. They will meet same time next Friday. Frank will email him the materials meant to cover tonight. In the future, David needs to inform Frank about canceling at least 24 hours in advance. 