When I ran a full-time school, we had three levels of instructors.
Apprentice instructors received no specialized training, but were there for other instructors to lean on in a "Mr. Brown Belt, please review what I just taught with the white belts while I work with the blue belts" kind of way.
Assistant instructors went through an 8-week training course on how to drill, plan drills and keep class safe. They would be responsible for a subdivision of class if the lead instructor felt it was necessary.
Instructors went through an additional 12 weeks of training on curriculum, pedagogy (learning theory), first aid and motivation. After completing that training, an instructor was qualified to take responsibility for an entire class.
Not tang soo do, but I figured I'd stick my nose in.