Harper Lee does not focus much on physical descriptions of Scout and Jem in To Kill a Mockingbird, at least not directly. Rather, she weaves hints of physical characteristics into a narrative that focuses mostly on their intellectual and emotional growth.

That said, though, we can develop a mental picture of Jem through the author's hints. Jem is between ten and twelve years old when the story takes place. He is an active boy, interested in sports and games and always ready to play outside. He has a slender build and isn't especially tall (which isn't unusual for boys of his age). He is quick and nimble, however, able to run fast and climb under and over things, even wiggling himself free when he caught on the Radleys' fence. Jem has straight brown hair that tends to hang down, as Scout notes when she compares him to Boo Radley's soap figure.

In chapter 11, we receive another detail about Jem. When he is angry, as he becomes at Mrs. Dubose's insults against Atticus, Jem turns bright red. Therefore, he might have fair skin. Indeed, this physical detail (turning red in the face) reveals something about Jem's temperament. He is a feisty young man who has a quick temper, and Atticus helps him learn how to control it by sending his son to read to Mrs. Dubose every afternoon for a month.

In chapter 11, Jem’s physical description is that of a naïve, young boy. Jem’s age is not entirely clear in chapter 11; however, it is certain that Jem is either nearly 12 years old or almost 12 years old. The only physical description Harper Lee provides of Jem in chapter 11 is that he “turned scarlet.” This physical descriptor is a result of the conflict between Jem and Mrs. Dubose, which  frames chapter 11.

The conflict begins when Mrs. Dubose fires a verbal attack on Atticus. Mrs. Dubose facetiously proclaims, “what has this world come to when a Finch goes against his raising?...Your father’s no better than the niggers and trash he works for!” At these words, Jem turns scarlet and, prompted by Scout, walks away. Later that afternoon Jem and Scout return to Mrs. Dubose’s house. As they pass the house, Jem snatches Scout’s newly purchased baton out of her hand and runs “flailing wildly up the steps into Mrs. Dubose’s front yard.” Infuriated, Jem “did not begin to clam down until he had cut the tops off every camellia bush Mrs. Dubose owned, until the ground was littered with green buds and leaves.” The act is quite uncharacteristic of Jem, who is normally level headed and calm.

When Atticus learns of Jem’s outburst, he forces his son to return and “have a talk” with Mrs. Dubose. Jem agrees to clean up the mess he has made and to work every Saturday to try and make the camellias grow back. Additionally, Mrs. Dubose has requested that Jem come every afternoon after school and on Saturdays to read aloud to her for two hours. Jem protests and begs Atticus to relent. Jem begins reading to Mrs. Dubose every day and Scout accompanies him. The children are startled at first because Mrs. Dubose has afternoon fits that leave her slightly unconscious.

The narrative jumps forward a month and Scout realizes that every day she and Jem had stayed a little longer at Mrs. Dubose’s house and that the old lady’s fits were gradually passing off. Finally, one afternoon, Mrs. Dubose said, “’That’ll do…And that’s all.’” With that, the children “bounded over the sidewalk in a spree of relief” of having been released from their burden. A month later, Atticus brings the news that Mrs. Dubose has died and that her fits were related to her morphine addiction. Knowing that she would die soon, Mrs. Dubose had undertaken to break herself of the addiction. She leaves Jem a “white, waxy, perfect camellia.”

Atticus explains to Jem that Mrs. Dubose was “the bravest person I ever knew.” Jem learns that real courage is knowing “you’re licked before you begin but you begin anyway and you see it through no matter what.”

Thus, while physical description is important in chapter 11, Jem’s emotional development is perhaps the focus of the chapter. At the end of the chapter, readers witness Jem come to terms with reality and to recognize that courage is not always “a man with a gun in his hand,” which is a reference to Atticus shooting the mad dog. Rather, courage is fighting for what is right and honorable, despite public opinion.

Jem is an adolescent boy who is active and athletic.  He has brown hair and is not very tall, but has a thin build.

Jem is ten years old when the book starts.  We also know that he has straight brown hair from the description of Boo’s model of him.

The boy had on shorts, and a shock of soapy hair fell to his eyebrows. I looked up at Jem. A point of straight brown hair kicked downwards from his part. I had never noticed it before. (ch 7)

Jem also has light skin, which turns red when he is embarrassed.  Jem is also fit and athletic.  He loves sports.  Scout describes him as “football-crazy” (ch 10).  The first sentence of the chapter refers to his reaction to breaking his arm, saying that he was just happy he could still play football.

However, Jem is not very tall.  When they visit the Radley house, Scout notes that the window “sill was several inches taller” than Jem (ch 6).  Jem is fast though.  He spends most of his time active.