While I agree that kits would be convenient, especially if a class is not taught at a shop, what if they are not to the students' tastes? Would people opt out of taking a class if they don't like the colors that would be used? Perhaps not as much an issue for beginners, though.
Having an instructor not be available and teaching the whole class would be irritating! If an instructor is willing to help students select materials or prep materials, that should happen before the class begins. At a shop I used to go to, teachers were available an hour ahead to meet anyone who was unsure about fabric selection. In the case of the dyeing class, if the option is to bring your own or purchase through the teacher, that choice should be made clear when registering, so that the teacher can have the amount needed prepared and paid for ahead.
Good luck!