How does Dill change from the start to the end of Harper Lee's To Kill a Mockingbird?

At the start of Harper Lee's To Kill a Mockingbird, Dill is young, energetic, and imaginative. His youthful innocence is portrayed in the fact that he is the only one of the three children who cries during Tom Robinson's cross-examination by Mr. Gilmer. However, by the time Dill accompanies Jem, Atticus, and Calpurnia to Helen Robinson's home to inform her of her husband's death, we see he has lost all imagination and strong emotions.

Dill's energetic imaginativeness is reflected in all the games and stories he makes up. One example is seen when, on the night he is discovered having run away from Meridian to Maycomb, he tells Scout a story about where babies come from. According to Scout's narration, Dill tells her, "There was a man [he] had heard of who had a boat that he rowed across to a foggy island where all these babies were; you could order one--" (Ch. 14).

During the trial, when Dill cries because he feels Mr. Gilmer is treating Robinson horribly, Mr. Dolphus Raymond says he understands why Dill is crying; it's because such treatment "just makes you sick, doesn't it?" (Ch. 19). Yet, Mr. Raymond also warns that as Dill grows up, "[H]e won't get sick and cry" (Ch. 20). He'll realize something is wrong, but it won't make him cry any longer. By the time we learn about Helen Robinson's reaction to her husband's death, we see that Mr. Raymond's prediction was correct and was even fulfilled much sooner than we would expect.

We learn of what Dill recounts to Scout of Helen's reaction through a flashback Scout has one evening after Dill had returned to Meridian at the end of summer. Through Scout's flashback, we learn that Dill's story was extremely truthful and straightforward; he did not embellish the story in any way, as he normally would have done. He described black children playing marbles in the front yard. He also described a young girl's hair as being full of "tiny stiff pigtails, each ending in a bright bow" (Ch. 25). Most importantly, he described Helen as falling to her knees without even being told the bad news. What strikes the reader is that Dill does not cry while reciting this story even though the story is full of the consequences of social injustices.

The fact that, by the end of the book, Dill tells a straightforward story without any embellishments and does not cry despite the fact that the details of the story are tragic shows that, as a result of witnessing the trial, Dill has lost his innocence and has become hardened. As a result of losing his innocence, Dill loses his imaginativeness and some of his sensitivity.