Shirley Jackson, in her short story "Charles," details the story of a little boy just starting school. The similarities between his behavior and Charles' behavior at home are very similar (which allows the engaged reader to realize, far before the end, that Laurie is Charles).
Multiple times in the text, Laurie's behaviors are very questionable. On his first day of kindergarten, Laurie leaves the house already a different person. Laurie's mother describes to readers the immediate difference between her pre-kindergarten boy and the boy leaving for school.
My sweet-voiced nursery-school tot replaced by a long-trousered, swaggering character who forgot to stop at the corner.
Already, her son has changed. This changes becomes even more apparent when Laurie returns home. The normally quiet (assumptive based upon the mother's tone) boy is now "raucous" and shouting. This behavioral change is denoted by the use of the word "suddenly." It is as if Laurie's behaviors immediately changed the moment he began his first day of school.
As the week went on, Laurie spoke "insolently" to his father, had used the Lord's name in vain, and been destructive. (These are all behaviors the reader can assume have come with his attending school.)
Laurie's behavior at home is very similar to Charles' behavior at school. Charles is loud, disrespectful, and hard to manage. As readers finish the text, they (as well as Laurie's mother) come to realize that Laurie is Charles. Essentially, Laurie's behaviors at home are so similar to Charles' that engaged readers are sure to pick up on the similarities.