Just want to put in my two bits. I had two friends that wanted to learn to quilt so we decided they would make a Christmas table runner and we would do it once a week for 4 hours each time at my house and it would only take 8 hours. We did that and it worked great, now we have moved onto a lap quilt.
The problem is I didn't charge them anything, they used my supplies if they didn't have certain things, I made them lunch while they were here and now they are already telling me what want to make next.
I enjoy being able to show people how to quilt but feel I am being taken advantage of a bit. I will be telling them that from now on there will be a fee for the project and I will figure out how long it should take them to do it and organize our "Classes" that way.
Make sure you charge something right from the beginning.