Hi,
First I think all charges should be clear and up front.
Second I think ground school should be charged for especially if the instructor is paid on a per hour basis. After all you pay your plumber from the time he leaves home, not just for the time he has a spanner in his hand.
I always charge for the long briefs (Circuits, PFL, NAVx, Complex conversions) because to do them well takes a good few hours and I'd rather be flying than sitting in a classroom on a hot day. As someone pointed out £20 on good ground school saves more than that in the air.
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