How does Jason overcome his stammer by the end of the book?
In many respects, Jason overcomes his stammer through embracing words of counsel that others have given to him. Advice that he has received from older people help Jason embrace his identity and, as a result, he overcomes his stammer.
One individual that gives him advice that resonates in his identity formation is Madame Crommelynck. She tells him that his artistry rings more valid when he is authentically himself and not trying to be someone else. At the same time, such advice converges with the words that his speech therapist offers to him about his stammer:
Back in Durban I had a friend who'd once been an alcoholic. One day I asked him how he'd cured himself. My friend said he's done no such thing. I said, 'What do you mean? You haven't touched a drop in three years!' He said all he'd done was become a teetotal alcoholic. That's my goal. To help people change from being stammering stammerers into nonstammering stammerers."
In configuring Jason's stammer as something that exists within his own mind and seeking to "understand it" as opposed to "will it out of existence." The stammer is shown to be something psychological, something that lives in his own mind.
Mitchell constructs a reality in which Jason must come to terms with his own identity. This allows him to overcome his stammering. When Jason is immersed in the woods of Black Swan Green, he is in the midst of a world where he has to come terms with his own familial identity as well as his own fears. It is at this point, upon understanding the nature of what appeared to be unknown and dangerous, that he overcomes his stammer. In standing up to Ross Wilcox, further evidence of gaining mental strength is evident. As a result, Jason overcomes his stammer because of his ability to "understand" his identity in a more authentic manner.
Jason emerges as being able to reconcile the vision of external expectation as well as his own notion of self. In being able to not be so driven to "will it out of existence," and understand the collision between both realities, Jason emerges as a stronger person. The result of this is overcoming his stammer. In understanding this world, Jason recognizes that "The world's a headmaster who works on your faults. I don't mean in a mystical or a Jesus way. More how you'll keep tripping over a hidden step, over and over, till you finally understand: Watch out for that step!" Being able to "watch out for that step" in light of who he is and who he wishes to be outside of the pain of external judgment is critical in the formation of his identity. It is this understanding that enables Jason to overcome a stammer that is shown to be mental and within his own mind.