At several of the places where I’ve taught, new instructors have shadowed experienced instructors for months before beginning their own classes. With the rise of the pre-choreographed class, I see this happening less and less on a formal basis. It still happens on an informal basis, though; I mentor quite a few new instructors for varying lengths of time.
I love taking other instructors’ classes. It’s not often that I get an opportunity since I teach so much, but I enjoy it whenever I can.