More like his father in demeanor, Jem is of a more pacific nature than the feisty Scout. He also is much more reasonable; for instance, on the first day of school, it is Jem who intervenes to prevent Scout from avenging herself upon Walter Cunningham for what she feels is his contribution to her having her hand struck with a ruler by Miss Caroline. "Let him go, Scout. Why?" he asks her what her motivation is for attacking Walter. Jem, then, apologizes to Walter, and recognizing him as the son of one of Atticus's clients, he invites Walter to lunch at their house. Scout narrates that "when Walter caught up with us, Jem made pleasant conversation with him."
Jem is honest: After Scout finds a small box fashioned from chewing gum wrappers in the knot-hole of a Radley tree. Once home, Scout asks Jem what they should do.
"We'll keep 'em till school starts, then go around and ask everybody if they're theirs. They're some bus child's maybe...They've been saved."
Yet, while he exhibits some maturity, Jem is still a boy and has his suppositions about Mrs. Dubose's mean character and about passing by "Hot Steams." Jem says when one walks by, he has to say, "Angel-bright, life-in-death; get off the road, don't such my breath."
Jem also sneaks up to the Radley porch even after Atticus has warned them to mind their own business.
He still maintained, however, that Atticus hadn't said we couldn't, therefore we could; and if Atticus ever said we couldn't, Jem had thought of a way around it: he would simply change the names of the characters and then we couldn't be accused of playing anything.
In the next chapter, after Dill fabricates the loss of Jem's pants as the result of their playing strip poker, Atticus asks if they were playing with cards.Using his young lawyer mind,Jem tells Atticus that they were not playing with cards, but with matches instead, mitigating the offense as "cards were fatal" since cards suggest gambling. Later, however, Jem's conscience is guilty and he says, "We shouldn'a done that tonight, Scout."
In Chapter 7, Jem begins to mature; he perceives Boo Radley as a person and writes a thank you note for the gifts from the knot hole. "Dear sir--We appreciate...everything you have put into the tree for us..."
As he grows older, Jem begins to think that his father is weaker than other fathers because he will not engage in tackling him in football, and when he gave them their air-rifles, he refused to teach them to shoot. But, after he takes careful aim and shoots the rabid dog, Jem acquires a new admiration for his father. He tells Scout not to mention this sharp shooting by Atticus because "...if he'd wanted us to know it, he'da told us. If he was proud of it, he'da told us."
Atticus is real old, but I wouln't care if he couldn't do anything--I wouldn't care if he couldn't do a blessed thing....Atticus is a gentleman, just like me!"
As he matures, Jem feels superior to Scout, telling her, "...you antagonize Aunty and I'll--I'll spank you." Breaking "the remaining code of [their]childhood," Jem tells Atticus that Dill has snuck into the house in chapter 14.
In the next chapter, Jem rushes to protect his father at the jailhouse. When Atticus tells him to go home, Jem refuses, shaking his head. Scout observes about Jem,
As Atticus's fists went to his hips, so did Jem's, and as they faced each other I could see little resemblance between them: Jem's soft brown hair and eyes, his oval face and snug-fitting ears were our mother's, contrasting oddly with Atticus's graying black hair and square-cut features, but they were somehow alike. Mutual defiance made them alike.
During the Tom Robinson trial, Jem is protective of Scout, explaining some things, and letting others go past her. He tells Reverend Sykes that Scout cannot follow the trial entirely, "She doesn't know what we're talking about." But, after the trial, it is Jem, not Dill, who cries at the injustice done Robinson. "How could they do it, how could they?" Thus, becoming a little cynical about human beings, Jem wonders why people are so divisive. Scout argues that there are just one kind of people; however Jem counters,
"That's what I thought, too," he said at last, "when I was your age. If there's just one kind of folks, why can't they get along with each other? If they're all alike, why do they go out of their way to despise each other? Scout, I think I'm beginning to understand something. I think I'm beginning to understand why Boo Radley's stayed shut up in the house all this time... it's because he wants to stay inside."