Teaching design must be one of the more difficult disciplines to master - it's less nebulous than art but far from as concrete as a science. Industrial design website Core 77 offers useful advice to putative design instructors in a feature entitled Those who can, teach.
Although clearly aimed at industrial design, much of the advice is useful across design disciplines - and perhaps even for creative directors who've taken on new talent fresh out of college.
You don't teach a class. You teach a group of individuals. Whether it's a lecture or studio or seminar or fieldtrip, you must never forget that you are teaching unique students who happen to show up at the same time and at the same place.