I think kits are a great idea. I would consider not making it an option, just bundle the kit price into the cost of the class. With everyone working with the exact same materials, the class will be easier to teach. It's easier saying 'take the red plaid square' rather than 'take the piece that you have cut into a 4 1/2 inch square', especially if there are several similar cuts. I have attended classes where the kit was not optional. I will say that those classes were technique classes as opposed to making a specific project, but I thought it really worked well. Also, I would think that many people would welcome the idea of just showing up with no prep work.