Workgroup approach

We actually do most of our training that way... instructors almost always take part in whatever the class is doing. For thinks like kata and kihon, we usually stand at the corners of the practice floor so that someone can see an instructor wherever they happen to be.

For anything interactive, like drills, pad work, bunkai and the like, we participate like anyone else; the only real difference is that we float around to different people, mostly by whoever looks like they need help with something.

For kumite, we put on the pads with everyone else. In fact, we usually have beginners do kumite with instructors, simply because a) instructors should have enough control not to hurt the beginner; and b) instructors should have the competency to avoid being hurt by a beginner who lacks control.

We occasionally fall back to the "guy up front" model if it's a special lesson, or a guest instructor - or it's a multi-club seminar for our organization, things like that.

Couple of hints...

1. Have a plan; know what you're going to cover, and for how long. It's easy to get lost in the moment and run out of time when you're actively involved.
2. Pay attention to your students; it can be harder to tell when someone is lost, or isn't keeping up with the rest of the group.
3. Make sure you can do what you're planning to teach. For example, if you've got a particular application you want to show, make sure you've practiced it beforehand. Don't be there trying to remember how it works, or fumbling around trying to make it work.
4. If you're doing something with contact, or especially something that involves falling, make sure to keep lower ranked students in mind. Just because you can toss your brown belts across the room because they know how to fall properly doesn't mean your white belts should be trying it that way. This too can be harder to detect when you're in the middle of things.
5. Mix it up. This is related to #2 but don't just work with your favorite students; make sure you go around to others, especially the less experienced folks.
6. Also related to #2 and #5 it helps to put additional effort into making sure you have senior students who can help you with all of this stuff. If nothing else, let them be your eyes and ears on the lookout for problems.

That is generally how my late Sensei would handle advanced classes, unless he was specifically focused on checking our form. He would periodically walk around to check on how people were doing, but he would mix in throughout the class, as well.

This is the way. Teacher's sweating their ass off. It's what my teacher does and what he says about Otsuka sensei. "Did you see who was the sweatiest guy in the room?" Smiling. He hates teachers with a dry dry dogi at the end of training.

Teachers should leed by example. Walk around and participate about 50, 50. And get hit in sparring.

here is what i have done when im in charge of classes in the last few months. there is sort of a basic structure for the overall class. then i and each of the sensei or senpai run a particular part of the class. warm up flexibility. kumite kata or whatever. when im not in charge of that part of the class i try to stand as back as possible behind all students facing who is currently leading. this allows me to train as well.