We see Jem begin to act like an adult when he and Scout were watching the Tom Robinson trial. And he strongly believes that Tom Robinson will not be found guilty because their father has been able to provide the jury with reasonable doubt. An example of this evidence is that Tom could not have beaten Mayella because he has no use of his left arm because he got it caught in a cotton gin when he was younger. When the jury had reached their decision and the Judge read each of the jurors decision of “Guilty ...guilty ...guilty ...guilty … [Jems] hands were white from gripping the balcony rail, and his shoulders jerked as if each guilty was a separate stab between them.” (Lee). So at the end of the day southern racism wins the case for the Ewells and Jem learns that even though the evidence is there, and there is reasonable doubt, people still vote for what they have been raised to believe, in this case it is that blacks are inferior and it is better for a black man to go to jail and get killed than a white man.
As you can see Harper Lee expressed her experience as a southern child in the nineteen thirties through writing her novel To Kill A Mockingbird. She used those experiences to develop the theme of everyone will lose their innocence at a point in their life. She shows the transition of acting like a child