Hmmmm Frank. To my way of thinking... wouldn't one have to have the same credentials to be a sub teacher as one would to be a full time teacher? I really dunno. Seems reasonable to me. I would think the teacher unions would cry foul if he didn't.
Then again maybe he had a 24 business hour exemption. 
Nope.
At least at the time the Bostonian Drunkard was a
substitute teacher, the laws of Massachusetts were similar with the laws here in Nebraska, in regards to temporary teachers. Probably it's still the same way; I cain't imagine there's any reason it'd bee changed.
To be a
substitute teacher in Nebraska or Massachusetts simply requires a bachelor's degree in
some area.
A simple four-year college degree will do it, but of course there's severe limitations on what one can do, and it's low-paying, so many don't do it. Also, one gets no benefits, just the daily pay.
The Bostonian Drunkard has a four-year college degree in English literature.
One has to have a four-year college degree in "education" to be an official teacher.
I guess in Missouri the standards for substitute teachers are even more minimal.