Why do you think Laurie is Charles? Why do you think Charles acts out like that?
It is evident from the very beginning of the narrative that the mother's little darling is not the "sweet-voiced, nursery-school tot" that she imagines. Instead, like the imaginary Charles, Laurie is rude, impudent, and disrespectful.
Laurie's mother narrates that he "forgot to stop at the corner and wave goodbye" to her on his first day of school. When he returns home after his first day, he slams the door. At the same time, he throws his cap on the floor and shouts, "Isn't anybody here?" Laurie demonstrates that it is his own habit to be loud and rude. Indeed, it would be rare for a child to learn this behavior in just one day and then carry it out in such a bold and confident way—unless his parents usually allow such behavior at home.
"At lunch, he spoke insolently to his father and spilled his baby sister's milk," but he is not scolded. Laurie contends that his teacher has said his parents "were not to take the name of the Lord in vain." This phrase of Laurie's indicates that it is he who has used the Lord's name at school; he then excused himself by telling his teacher that his parents say the same thing. Again, there is no discussion with their child about his behavior on the part of the parents. The only correction that Laurie's mother makes to her son is grammatical. He says, "I didn't learn nothing," and his mother tells him he should have used "anything" rather than "nothing." However, she fails to question him about why he has not learned anything and what he has been doing instead of learning. As another example of the mother's obtuseness, she asks her son a question about the "awfully fresh" boy named Charles, but Laurie ignores her and leaves the room without any reprimand from his mother. In the meantime, "His father was still saying, 'See here, young man.'" For some reason, his parents do not reprimand Laurie for his disrespect and rudeness in rising and going from them into another room.
Laurie may behave as he does for attention. Sometimes, children unknowingly want to be disciplined because they are aware that their acts of misbehavior are inappropriate and normally unacceptable. They understand that a parent who cares about them would desire that they behave properly.
Author Jackson used several phrases and clues in the story to let the reader infer that Charles is really Laurie, or rather a figment of Laurie's imagination. On the first page of the story, when questioned by his parents about Charles' misbehavior the author writes that Laurie answered "...addressing his bread and butter..." rather than by answering his parents directly while looking at them. Laurie then walks off rather than answer his parents.
Later in the story, Laurie arrives home late full of stories about Charles' antics and states that Charles had to stay late after school for his misbehavior. Ironically, his parents do not seem to realize what the reader immediately sees in that connection.
Lastly at the end of the story, Laurie's mother meets his teacher and mentions Charles' disruptions. His teacher replies that there is not a "Charles" in class. Obviously, Charles acts out as he does due to Laurie's actions since they are one in the same. Laurie has a strong character and is independent enough to want to experiment, as a kindergartner, with who he really is. He is experimenting with different personalities, perhaps to get his parents' attention, perhaps even to get into enough trouble to have to stay home.