All I'd add to that discussion is that in our organization -- The Australian Jiu-jitsu, Judo, and Chinese Boxing Federation of Instructors -- I don't think you can make it to black belt without an affinity for teaching. As the name indicates, there's a lot of teaching in our system, and by developing everyone into teachers as well as martial artists there's a lot more hands-on instruction available than if teacher status is reserved for a select few.
Anyway, there's another dimension I'd like to explore. The next step after doing some occasional class teaching -- typically stepping in occasionally for the full-time instructor -- is to start your own regular class. In our organization this means that either you inherit and existing class or start a new club.
While this is something I recommend, you wouldn't want to rush into it. I've just completed year 5 with my own club, and even only running one class a week (a two hour class, though!), it's a lot of work: Class planning, answering enquiries, record-keeping and collecting dues, maintaining equipment, liaising with the venue owners, submitting grading recommendations, advertising, scrutinizing candidate students. There's a lot to do, and there's work and family life too, but once some simple systems are in place, most of that stuff becomes quite routine. Blogging, by the way, should be strictly optional.
Oh, and there's teaching, too. That's the fun bit!
It never rains, but it pours. After four years of running my class on a Monday night I switched in 2009 to Wednesday and suddenly I went from a handful of students -- typically 3 to 6 per class, sometimes less -- to more typical class sizes of 8 to 12, peaking at about 14.
There's a lot less hands-on instruction by me on each and every student now. The students who remain from earlier times sometimes say they miss that, but there's now more energy and camaraderie on our now crowded mat. And next year should be that much better, with a core group who train week-in week-out solidifying.
Next step may be to increase the mat area!
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Teaching someone else's class or running a short course is a bit like doing some baby-sitting as an uncle or aunt: hard-work, hopefully fun, but you get to give them back. Starting your own class and/or club is more like parenthood; it's something you need to be ready for, and it's definitely not for everyone.
I highly recommend putting in a few years as an assistant to someone else first.