Much is learned in the first part of Harper Lee's To Kill a Mockingbird.
When Charles Baker Harris, known as Dill, arrives in Maycomb, Scout and Jem learn that Dill does not know his father. As they become more acquainted, Scout and Jem realize Dill is very creative and he is familiar with many movies and novels. Dill himself learns about the Radley house and the "haint" inside, where Mr. Radley is dying.
When school begins, Dill returns to Mississippi and Scout begins first grade. Although Jem has warned her, Scout becomes very disappointed in the reality of school and learns that her ideas about school have been very unrealistic. Her teacher, Miss Caroline, scolds her repeatedly for her accomplishments, hurting Scout's feelings. From these scoldings, Scout learns how preconceived ideas about what things should be like can be harmful.
Jem invites Walter Cunningham to have "dinner" with them at noon. Scout voices her disapproval of the way he eats. Calpurnia takes her into the kitchen and scolds her for being discourteous to a guest. Scout is made to eat in the kitchen, where her lesson of learning to be polite to her guest(s) sinks in.
That evening she begs her father to let her stay home after she relates how Miss Caroline has scolded her about knowing how to read and write cursive. Atticus explains that he cannot teach her because he must work. Further, he instructs Scout about how important it is to try to "climb into [the] skin" of others and see things from their perspective.
To make Scout feel better, Atticus suggests a "compromise": they can still read together at night, but Scout must not say anything at school. Scout learns a little more about the adult world.
Dill arrives from Mississippi, full of tall tales. Later on, the boys put Scout into a tire and send her rolling. She lands in the Radley yard, right before the steps, and she hears laughter, so Scout learns that someone real is inside. Later, they re-enact a scenario from Boo's youth.
Having been warned not to re-enact scenes from the Radleys, Jem declares that they can just change the names of the characters, and then Atticus will not know that they are ignoring his order to stop bothering the Radleys.
Later on, Scout meets Miss Maudie, who is often outside tending her lawn or garden. From this kind lady, Scout learns that Miss Maudie has known her Uncle Jack for many years; Miss Maudie also knows the history of the Radleys. In response to Scout's inquiry as to why Arthur Radley has not come out in public, the woman asks, "Wouldn't you stay in the house if you didn't want to come out?" As Scout considers the matter, Miss Maudie explains that Mr. Radley believes that "anything that is a pleasure is a sin." Scout learns that the Radley house is "a sad house" because Arthur Radley has lived in a rigid and repressive environment.
Dill and Jem persist in their attempts to make contact with Boo Radley. According to Jem,
Dill and Jem were simply going to peep in the window with the house shutter to see if they could get a look at Boo Radley....
But when Jem goes around to the back of the house and he puts his foot on a step, it creaks, and someone comes outside. Jem races to Dill and Scout, and they learn theirs could have been a deadly game since Nathan Radley has a shotgun.
Then the shotgun blast brings out the neighbors, and Atticus discovers that Jem is missing his pants. The glib Dill states that Jem and he were playing strip poker, and Jem adds to this lie with another as he says they were playing with only matches, not cards.
That night as they sleep on the porch, Scout hears Jem, who is going to try to retrieve his pants. He informs Scout that Atticus has never caught him in a lie, and he does not want Atticus to know that he has been false to him. Therefore, he must return to find his pants. When he comes back to the porch, Scout notices how hard he breathes on his cot.
Jem has learned the cost of a lie is usually higher than that of telling the truth.
In the fall the children return to school, and when they pass the Radley tree on their walk home, they discover some artistically carved soap figures that resemble themselves. Thus, they learn that someone has been watching them and wishes to leave them gifts. That evening Jem writes a thank-you note that he tries to put into the knothole the next day; however, Mr. Nathan Radley has filled the hole with cement. Thus, they learn that Boo's family does not want Boo to communicate with them.
When there is a snow in Maycomb, there is great excitement because snow rarely falls there. With Scout's help, Jem fashions a snowman from dirt covered with snow. Excited by his creation, Jem shows it to Atticus. At first, Atticus compliments him; however, as he continues to gaze at the figure, Atticus realizes that Jem has had a model for his creation. He tells Jem that he has "a near libel here" and orders Jem to put an apron around the snow figure that too-closely resembles Mr. Avery. But Jem reasons that the figure will melt if he does this. So he rushes over to Miss Maudie's and returns with her hat, which he has placed on the snow figure's head. Jem has learned not to mock people.
That night Miss Maudie's house catches fire, and because of the freezing temperature, the old fire hose on the Maycomb fire truck does not work. The children are told to stand at the end of the block in front of the Radleys' place until it is safe to go inside. When they do return to their own house, Atticus wonders where the blanket on Scout's shoulders has come from. Then Scout learns that Boo must have put it on her because he was worried about her being cold.
When Scout learns that Atticus is being called names because he will defend the black Tom Robinson, who is charged with raping a white woman, Atticus informs her that it is his duty to defend Tom. It is his obligation to try to do his best for Tom.
Since it is the Christmas season, the Finches go to Finch Landing, where Aunt Alexandra prepares the meal. Jem and Scout's cousin declares that Atticus is ruining the family name. Later on, Scout hears her father talking with his brother Jack, who has asked him if he can avoid defending Tom Robinson. Atticus replies,
But do you think I could face my children otherwise? You know what's going to happen.... I just hope that Jem and Scout come to me for their answers....
Later, Scout realizes that Atticus wanted her to overhear him. In this way she has learned that one cannot sacrifice one's integrity. This lesson is the old "practice what you preach" combined with "be true to yourself."
When the children are given air-rifles, Atticus tells them that they can shoot bluejays, but they must never shoot mockingbirds. They learn not to harm innocent things.
Scout and Jem also learn that their father is an excellent shot. He shoots a rabid dog with one shot of the rifle. In this scene Jem learns that "Atticus is a gentleman, just like [him]" because he has always been such a skilled marksman that he felt he had an unfair advantage over the animals he shot—so he stopped hunting.