Hangman

I was curious about how autobiographical Black Swan Green is, so I looked up David Mitchell and was not super surprised to find out that he has a stammer. I guess this means that stammering wasn't chosen (at least not solely) as a plot element due to its propensity to represent more general adolescent issues, but I think it does this very well. There was certainly a distinct difference between how open I was about expressing my thoughts in 5th grade vs. how open I was about expressing them in 6th grade. Somehow the foreign everything of middle school and the increasing social complexity that comes along with adolescence made me more self conscious about how I was projecting myself to the rest of the world. So I edited my speech, my posture, just like hangman forces Jason to edit which words he uses, and it really limited my communication (although not nearly as much as Jason is limited).
Like Unborn Twin, Hangman is personified as an independent entity inside Jason with its (his?) own desires and schemes to make Jason miserable. This seems an appropriate representation to me of some part of you that you have no control over and therefore doesn't quite feel like you. I can picture it, though I've never had a stutter.
Jason explains that he has dubbed his stutter "Hangman" because it first appeared when he couldn't get the word nightingale out during a game of hangman in class, but I think the fact that Hangman uses words to "execute" Jason's social standing probably also has something to do with it.
At the end of the book when he's talking with/at the old lady, he seems to make some progress in understanding Hangman. He decides that he doesn't cause it, rather the expectations of whoever he's speaking with do. So if he speaks with people/things that won't judge him, he does just fine, and that if he could stop caring, Hangman would go away entirely.  This is both probably true of stuttering and, I think, sort of representative of Jason's larger social issues in the novel. He finally overcomes his struggles with coolness not when he achieves it but when he stops caring about it. And, in fact, this causes him to be perceived as cool to some extent (or at least not to be teased mercilessly).
I was kind of expecting Jason to kick it by the end of the novel and I think the fact that he doesn't reinforces the idea that his development as a character isn't over. It also made his (fairly abrupt) transition into a confidence in his social standing more smooth. I also take it that Mitchell himself still doesn't have Hangman completely under wraps and that is he still somewhat embarrassed about it "I'd probably still be avoiding the subject today had I not outed myself by writing a semi-autobiographical novel, Black Swan Green, narrated by a stammering 13 year old."