Young Laurie begins school, in Shirley Jackson's "Charles," and immediately comes home to regale the family with daily reports about Charles. Charles seems like a total monster, and it raises questions about the creation of Laurie's "Charles." Through all of the terrible behaviors that Charles exhibits, the biggest surprise, of course, is that Laurie is Charles.
One interpretation is that Laurie suffers from dissociative personality disorder. This is another way of saying that he has a split personality—in other words, that two separate personalities exist in his body. There is not enough evidence to support this theory with any certainty.
Personally, I believe that Laurie, as Charles, is spreading his young wings to see what he can get away with. We can infer that he does not behave at home the way he does at school, or Laurie's parents would immediately be suspicious of similarities between Laurie and Charlie.
At dinner one night, Laurie plays an old game with his father. Telling his dad to look up, then down and finally at his thumb, Laurie announces, "Gee, you're dumb." Then Laurie...
...began to laugh insanely.
This behavior must not be new in that his mother does not stop or scold him, but moves on. Had she been concerned, we could guess that she was seeing something unrecognizable and unpleasant in her son. If it has happened before, his mother is not going to address his behavior, for the text says that she moves quickly to ask her son a question. One might wonder if going to kindergarten has caused Laurie to act out. His mom speaks to her husband about her concerns:
Do you think kindergarten is too unsettling for Laurie? All this toughness and bad grammar, and this Charles boy sounds like such a bad influence.
Her husband tells her not to worry, but one would have good reason to suspect that these new behaviors are the result of difficulty of entering school and being separated from his home and mother.
At the same time, Laurie may simply be unburdening himself anonymously to his mother and father. In this way he speaks of what Charles has done, but does not experience any reprimand for his actions.
More than suffering from any kind of psychological impairment, I believe that Charles is almost literally sowing his wild oats at school and unburdening his behaviors onto the fictional Charles. In this way Laurie is able to laugh about these things with his parents and study their reactions. To me, Laurie appears to be a very intelligent child who amuses himself as his teacher's and classmates' expense. Laurie seems to enjoy acting out as "Charles," perhaps manifesting these behaviors to draw attention to himself. For at home, he is the center of attention.
A hallmark of Jackson's work is to leave the reader surprised and unsettled. She usually addresses serious issues. Her work certainly raises a multitude of questions. While Laurie may be an artful liar, I do not think he has a personality disorder. More likely, he is a child that needs to be kept busy and fully occupied at all times.