I am a second kyu, and I teach the advanced junior kumite class (13-16) whenever the sensei can't be there (about every other week). I was asked to do this because I am one of the few young guys at the dojo who consistently wins tournaments, and the teacher wanted a younger guy to help him teach the young students.

Teaching is HARD at first. It can be very akward, such as when you explain something, and everyone looks at you like they have NO idea what you just said.