Jem and Scout are depicted as typical siblings who bicker and fight on occasion but genuinely love and support each other. Scout looks up to her older brother, and Jem is portrayed as a caring, enthusiastic older sibling. Jem spends a considerable amount of time with Scout and allows her to tag along on his adventures with Dill. Similar to many older siblings, Jem has a tendency to dismiss Scout's feelings and get on her nerves.

As Jem begins to experience puberty, he becomes more aloof and domineering. In chapter 14, Harper Lee illustrates their typical sibling rivalry by depicting Jem and Scout's altercation. Scout expresses her negative feelings towards Jem by saying,

His maddening superiority was unbearable these days. He didn’t want to do anything but read and go off by himself. Still, everything he read he passed along to me, but with this difference: formerly, because he thought I’d like it; now, for my edification and instruction. (73)

Despite their sibling rivalry and minor disagreements, Jem and Scout have a close relationship and are genuinely concerned about each other's well-being. Towards the end of the story, Jem matures into a respectful, sympathetic adolescent and demonstrates his love for Scout by comforting her after the Maycomb pageant. Jem recognizes that Scout feels embarrassed about her performance and goes out of his way to console her. Scout mentions,

He [Jem] said he couldn’t see my costume much from where he was sitting. How he could tell I was feeling bad under my costume I don’t know, but he said I did all right, I just came in a little late, that was all. Jem was becoming almost as good as Atticus at making you feel right when things went wrong. Almost—not even Jem could make me go through that crowd, and he consented to wait backstage with me until the audience left. (137)

Overall, Jem and Scout have a typical sibling relationship, where they bicker and argue sometimes but care deeply about each other. Following the Maycomb Halloween festival, the Finch children are attacked by Bob Ewell, and Jem attempts to save Scout from their attacker, which once again demonstrates his love for Scout.

Jem and Scout, an older brother and younger sister who are four years apart, have a close relationship that evolves over the course of the novel. Scout and Jem are especially close because they have lost their mother, which bonds them tightly together.

Jem, as the older brother, is bossy and sets the pace of the relationship. Because she wants to emulate and keep pace with him, Scout takes on a boyish demeanor, wearing overalls and becoming a scrappy fighter. She wholeheartedly rejects traditionally feminine ways and activities.

Jem's entry into adolescence coincides with the Tom Robinson trial, and Jem takes the confirmation of injustice that the trial represents very hard. He begins to pull away from Scout as he gets older, and the adults advise Scout to let Jem have his space as he works out his issues.

Despite Jem's changes, however, the two remain close. They have both been molded by Atticus and both see the world in fundamentally the same way. They realize, for example, that they are much different from Aunt Alexandra. While Atticus invites Walter Cunningham over to dinner early in the novel, Aunt Alexandra refuses to allow Scout to play with him, asserting that he is white trash and his ways will rub off on her. When Scout reacts with fury, Jem, despite his early adolescent angst, understands how Scout feels and knows how to comfort her:

I don’t know what I would have done, but Jem stopped me. He caught me by the shoulders, put his arm around me, and led me sobbing in fury to his bedroom ... “Have a chew, Scout.” Jem dug into his pocket and extracted a Tootsie Roll.

Whatever quarrels they might have, Jem can be relied on throughout the novel to be on his sister's side, just as she is on his.

The relationship between Scout and Jem in To Kill a Mockingbird changes throughout the novel as the characters, particulary Jem, grow up. They experience exciting, upsetting and dangerous events and these help to develop the way they relate to each other.

In chapter one, page one, Lee begins the story by using foreshadowing as Scout recounts the causes of their adventure. She says: 

'When enough years had gone by to enable us to look back on them, we sometimes discussed the events leading to his accident. I maintain that the Ewells started it all, but Jem, who was four years my senior, said it started long before that. He said it began the summer Dill came to us, when Dill first gave us the idea of making Boo Radley come out'.

This quote gives us some idea of the way their relationship with each other developed after the story ended. They communicate well as brother and sister while Jem's role as the older brother, a role which he tried to perfect throughout the novel, is evident in his ability to recognise the significance of their initial encounters with Boo Radley.

The age gap between the siblings is interesting as it ensures that their roles in the story are definite; Scout as the curious, young, tomboy and Jem as the increasingly mature, yet rather emotional, older brother. However, despite these distinct roles, the edges sometimes blur. In chapter two Scout's narration tells us of their already changing relationship:

Jem condescended to take me to school the first day...I think some money changed hands in this transaction, for as we trotted around the corner past the Radley Place I heard an unfamiliar jingle in Jem's pockets...Jem was careful to explain that during school hours I was not to bother him, I was not to approach him with requests to enact a chapter of Tarzan and the Ant Men, to embarrass him with references to his private life, or tag along behind him at recess and noon. I was to stick with the first grade and he would stick with the fifth. In short, I was to leave him alone (Chapter 2).

Scout and Jem care about each other, even if they don't always agree with each other. Jem repeatedly talks about being 'gentlemanly' as though the more he says it, the truer it will become. Scout often recognises her brother's emotional reactions to events and gives him time to calm down and process things for himself, showing her own burgeoning reflective nature:

Jem stayed moody and silent for a week. As Atticus had once advised me to do, I tried to climb into Jem's skin and walk around in it: if I had gone alone to the Radley Place at two in the morning, my funeral would have been held the next afternoon. So I left Jem alone and tried not to bother him (Chapter 7).