ANSWER-
John has overcome a lot of things, and all of that has made him stronger. This helps develop the theme to overcome fears and stand up for ones self.
Summary-
At the end of the story, John is not as afraid as he used to be. John worried about a lot of things and he was also frightened a lot of the time. John says to his father "Watter never hurt a man; it keeps his hide from cracking." This says to me that John is very changed after his encounter with the other boy. John also says "Say, Pa! Will you chuck me your bull whip here ashore? Them horses is getting kind of dozy. They need soaping proper." John was scared that he would get in trouble for dropping his whip and he did not want to ask for his dads whip because he thought that his dad would get angry. John has matured and now he is acting like his dad was. I do not think that John and his father reversed positions, just that John has grown more like his father.
Hope this helps!