In The Yearling, how does Jody's ordeal of running away change him?

Jody begins his running away with something of a plan. He wants to run off to Boston to see Oliver and Grandma Hutto. He is consumed by the pain of his loss and unwilling to confront going home and what it will mean. At first he even tells himself that he is not hungry, that the smell of food doesn't hurt him much.

He works to come to terms with what has happened. He has to tell himself out loud that Flag is dead and that his father "went back on him."

He then begins to feel the real hurt of starvation. He begins to have cramps and feel the weakness and pain of real hunger. He also notices things that he still has things to learn from Penny, like starting a fire without a tinder horn. 

He then understands what his mother meant when she said that they would all go hungry if he didn't do something about Flag. He begins to understand her and her worry and her reasoning for shooting the fawn.

When he stops to build a flutter mill and then realizes it holds no joy for him anymore, he has accepted the responsibility of being a man. He is terribly sad for what he knows he has lost. This loss is confirmed once he gets home and speaks with his father. As he falls asleep, he cries out for Flag. But "It was not his own voice that called. It was a boy's voice. Somewhere beyond the sink-hole, past the magnolia, under the live oaks, a boy and a yearling ran side by side, and were gone forever."

How does Jody's coming of age unfold in The Yearling?

One of the first impressions the reader has of Jody is when he is building a flutter-wheel in the river rather than doing the work his father has asked him to do. He is grateful for the gentle way that his father allows him the freedom to explore and sometimes play when he needs to be working. His life is also relatively stable at this point and his responsibilities few.

That quickly changes when they cannot kill Old Slewfoot and he starts to understand more of the conflict with the Forresters and the complexity of their world. Jody sees his once strong and seemingly inexhaustible father nearly killed by a rattlesnake bite that leaves him weak and unable to handle the load that he used to.

Jody quickly begins to shoulder more of the responsibility but his link to his playful childhood is Flag, the fawn he has taken under his wing. Soon the fact that Flag is ruining crops and causing trouble starts to mirror the conflict that Jody has to face between staying a boy and becoming a man in the hard world.

At the end of the story when Jody has to kill the wounded Flag, he faces the hardness of starvation as he tries to run away from his responsibilities. He returns to the farm unable to see things the way he did just a year before. His maturation and the death of the child in him are in some ways a mirror of the death of his beloved Flag.