In the novel To Kill a Mockingbird, what are some quotes that show Jem losing his innocence?

At the beginning of Chapter 21, Jem has confidence that the jury will acquit Tom Robinson. He mentions to Reverend Sykes that there is no way the jury can convict Tom Robinson based on the contradicting testimonies and lack of evidence. Unfortunately, the prejudiced jury finds Tom Robinson guilty of assaulting and raping Mayella Ewell. Jem is devastated and begins to cry.

In Chapter 22, Jem repeatedly tells his father, "It ain't right." (Lee 284) Jem had witnessed racial injustice for the first time in his life and lost his childhood innocence after the guilty verdict was read. The next morning, Miss Maudie invites the children over to her house for some cake. Miss Maudie tells Jem not to fret and tries to explain that Atticus had a very rough job. Jem says,

"It's like bein' a caterpillar in a cocoon, that's what it is...Like somethin' asleep wrapped up in a warm place. I always thought Maycomb folks were the best folks in the world, least that's what they seemed like." (Lee 288)

Jem elaborates on his new perspective of Maycomb's community members. After witnessing their prejudiced beliefs in action, Jem becomes jaded about his neighbors. He is having difficulty understanding how caring, good-natured citizens can be so full of hate. 

In Chapter 23, Scout and Jem are having a conversation about why Aunt Alexandra will not let Scout play with Walter. Jem says, 

"I've got it all figured out, now. I've thought about it a lot lately and I've got it figured out. There's four kinds of folks in the world. There's the ordinary kind like us and the neighbors, there's the kind like the Cunninghams out in the woods, the kind like the Ewells down at the dump, and the Negroes." (Lee 302)

Jem is trying to explain to his younger sister the social class system of Maycomb. These are recent thoughts that have developed since he witnessed racial injustice during Tom's trial. Scout disagrees with Jem and says, "I think there's just one kind of folks. Folks." (Lee 304) Jem replies,

"That's what I thought, too...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 the time...it's because he wants to stay inside." (Lee 304)

Jem is still trying to make sense of why his neighbors treat each other with such contempt. Jem not only notices how white people treat black people terribly, but also notices the contempt between social classes. Unlike Jem, Scout is not jaded after losing her innocence and still maintains that humans are caring, equal individuals. Jem's loss of innocence has a profound effect on his perspective of the world and his community.