What is the plot of the story "Charles" by Shirley Jackson?

"" tells
the story of Laurie, a young boy who is just beginning kindergarten. The story is told from the
perspective of Laurie's mother, who witnesses incredible changes in her son during this period.
He is no longer a "nursery-school tot," for example, and kindergarten transforms him
into a "long-trousered, swaggering character."

Each night, Laurie
comes home from kindergarten and tells his mother and father about a child in his class called
Charles who routinely misbehaves. On the first day, Charles got into trouble for "being
fresh," for example, and on the next, he was punished for hitting the teacher. Charles
seems to be such a bad pupil that Laurie's mother wonders if kindergarten is too
"unsettling" for her son. Charles's behavior soon improves, however, and he becomes
the teacher's helper, but it is not long before he is misbehaving again and he becomes a sort of
"institution" in Laurie's household.

When Laurie's first
parent-teacher meeting comes around, Laurie's mother is keen to speak with Charles's family for
herself. In an ironic twist, however, she is quickly cornered by Laurie's teacher and is shocked
to find out that Charles does not exist. Charles and his many misdemeanors were, in fact,
carried out by her own son, Laurie.