I start my classes on time. I have a note with the sign up forms that says if you want help purchasing supplies, come a half hour early and I will help you, but I will not delay the class. When students start chatting (not just a little comment), I stop and wait for them to stop. This usually embarrasses them and they tend to be more quiet. I also tend to layer my teaching to their skill. While I emphasize the importance of 1/4" seams, I work with newbies on how to square up an imperfect block. I feel it is more important for them to enjoy the process. Skill level will improve with practice..+