I forgot to mention..... I think you should charge for instruction time and not be charging for the time they are sewing only. I've taught group classes and I usually show how to do some skill and then the students do a sample or little bit of the sewing. Then, they go home to complete that skill. Many people are very nervous about doing some sewing in front of others because they are just learning. Others want you to stand over every stitch and are afraid to do anything without your help. You will have to determine what the learner wants from you to determine whether to charge by the hour or by the project.