"Scout yonder's been readin' ever since she was born, and she ain't even started school yet" (8)
Jem thinks beofre he acts
"It's just that I can't think of a way to make him come out without him gettin' us. Besides, Jem had his little sister to think of" (17)
Jem takes a risk
"I'm goin' around to the side of the house, said Jem. We looked yesterday from across the street and there's a shutter loose. Think maybe I can stick it on the window sill, at least" (62)
In the begining of the book, we see Jem standing up or showing off Scout every chance he can. As shown in this quote when Dill is braging about how good he can read, Jem points out just how much better Scout can read, without even having a second thought about it. Althouhgh, through the book we see this part of Jem change.
Jem yells at Scout
"Scout, I'm tellin' you for the last time, shut your trap or go home-I declare to the lord you're gettin' more like a girl everyday" (69).
Looking at a picture of Jem, one wouldn't think he would care so much about his little sister but in reality, Jem does everything he can to protect Scout and if someone is mean to her, Jem deals with it. This shows that although Jem may not look like a very protecting brother, if you dig deeper, there is no telling the lengths he will go to to protect Scout.
Jem says to leave the treasure
"Somebody like Walter Cunningham comes down here every recess and hides his things-and we come along and take 'em away from him. Listen, let's leave it and wait a couple day. If it ain't gone then, we'll take it, okay?" (78)
Throughout this book, we see Jem change in so many ways. One way he changes as shown in this quote is he takes more risks. The old Jem wouldn't have wanted to send a note to Boo and he definelty would not be the one to put the not in the window seal. But the new Jem takes this risk and decides to write the note and give it to Boo, no matter the consequences.
Jem sits with the adults at Christmas
"At Chirstmas dinner, I sat at the little table in the dinning room; Jem and Francis sat with the adults at the dinning table" (108).
Although Jem loves his little sister, in this part of the book he also knows Scout can take care of herself and if she wants to hnagout with him then she has to act tough. This is yet another aspect of how Jem changes. Jem being harsher to Scout shows that he wants her to be able to make her own choices and be able to stand up for herself.
In the begining of the book, Jem would've taken whatever treasures he found in the knot hole. However, Jem has matured and tells Scout that maybe what they are finding is someone elses and they have to leave it for a couple days. By doing this, Jem is not only changing and maturing, he is being a good role model for Scout. This is another exaple of how Jem has changed.
The one point in the book when it is clear how much Jem has changed and matured is when he is allowed to sit at the adults table during Christmas dinner. Scout thought her and Jem would do this together but Scout isn't mature enough yet. It's no longer just the readers who notice how much Jem has changed, now, the adults and Scout have all noticed too.