"Charles," like Shirley Jackson's most well-known short story, "The Lottery," has a few surprises and, certainly, a surprising ending. Within the story, however, Jackson has left a fair number of clues that she has created a kind of Jekyll-and-Hyde story or, more precisely, a Jekyll-and-Jekyll story. Laurie and Charles, who appear as distinct characters throughout the story, seem to mirror each other so precisely that we begin to suspect, as Laurie's parents do not, that Charles is Laurie's alter ego.
Our first encounter with Laurie is, by itself, no clue to the story's ending, but it does foreshadow the behavior later attributed to Charles. After announcing his arrival from school with a "raucous shout," Laurie
spoke insolently to his father, spilled his baby sister's milk, and remarked that his teacher said that we were not to take the name of the Lord in vain.
Implicit in this description is that Laurie has taken the Lord's name in vain, but Laurie's parents assume, as they do with all of Laurie's explanations, that he is not the culprit. Later during this exchange, Laurie describes the boy Charles being punished for "being fresh. . . . He was awfully fresh." In hindsight, we understand that Charles's punishment is most likely Laurie's for having cursed, but taking the description at face value, we can also see that Laurie and Charles seem to have many traits in common.
On the second day, Laurie reports that Charles has been spanked because he hit the teacher. Laurie then says to his father,
"Look up," he said to his father. "What?" his father said, looking up. "Look down," Laurie said. "Look at my thumb. Gee, you're dumb." He began to laugh insanely.
This joke, which has no real humor, is meant to belittle his father and is, in effect, a metaphorical attack on his father, much like Charles hitting the kindergarten teacher. We also need to attend to Jackson's choice of words to describe Laurie's laughing "insanely," an unusual choice for describing anything related to (presumably) a six-year-old child.
In a third instance, Laurie comes home and "yelled all the way up the hill" that Charles was bad again. Charles's infraction? He had yelled so loudly in school that a student from another class had "to tell the teacher she had to make Charles keep quiet." At this point, the behavior of Laurie and Charles is identical—they are both yelling—but the culprit, of course, is still nominally Charles. Laurie, however, as he sits down to lunch, greets his father with "Hi, Pop, y'old dust mop," another insolent verbal attack on his father, completely consistent the behavior attributed to Charles in his attacks on schoolmates and other teachers.
At this point in the story, Jackson has provided enough clues for a cautious reader to conclude that Laurie and Charles are actually just Laurie, who has managed to divide himself psychologically into two equally antisocial characters.