At the end of Rumble Fish by S.E. Hinton, a drastic change (at least not one that we saw) had not taken place in Rusty. He tags along with his brother "The Motorcycle Boy", who is going to rob a pet store. Rusty remarks about how the local police department is not a big fan of either him or the Motorcycle Boy.
They slip into the store through the back, and The Motorcycle Boy gets to work. But he doesn't steal anything. He simply unlocks all the cages and attempts to set all the animals free. But, while they were working at this, somebody calls the police.
Despite the noise of police sirens and the flashing of lights outside the store The Motorcycle Boy makes no effort to get out of the store, even while Rusty pleads with him to leave. When The Motorcycle Boy stands up from unlocking a cage, he is shot and dies almost instantly.
Thats pretty much how the story ends. A change in Rusty isn't really noticed.