What are three clues Jackson gives that indicate that Laurie, not Charles, is the problem?

At first glance, Shirley Jackson's short story "Charles" seems to be a simple tale of a young boy convincing his parents that a fictional student is responsible for his own antics at school. However, much has been written about the complexity that may underlie Jackson's writing, including the fact that she based some of the exploits on real characters. Additionally, Jackson may have written "Charles" with the intent that the story mean much more than the words at face value seem to.

Jackson provided readers with several tips indicating that Laurie himself is causing the problems he attributes to Charles. Early in the story, Laurie tells his parents of Charles' antics but wanders off without answering his father's probing questions.

Laurie thought. “It was Charles,” he said. “He was fresh.The teacher spanked him and made him stand in the corner. He was awfully fresh.”

“What did he do?” I asked again, but Laurie slid off his chair, took a cookie, and left, while his father was still saying, “See here, young man.”

Laurie is again asked about Charles and reveals another of his antics. After the below exchange, he also tells a joke in which he says to his father, "Gee your dumb" as part of the joke. These reveal to the reader that there is much more than an innocent little boy to the personality of Laurie.

"The next day Laurie remarked at lunch, as soon as he sat down, “Well, Charles was bad again today.” He grinned enormously and said, “Today Charles hit the teacher.”"

Later in the story it is revealed that Laurie came home late from school with the following tale, at which point readers may wonder if Laurie is Charles since Laurie was late getting home.

"On Monday Laurie came home late, full of news. “Charles,” he shouted as he came up the hill; I was waiting anxiously on the front steps. “Charles,” Laurie yelled all the way up the hill, “Charles was bad again.”
“Come right in,” I said, as soon as he came close enough. “Lunch is waiting.”
“You know what Charles did?” he demanded, following me through the door. “Charles yelled so in school they sent a boy in from first grade to tell the teacher she had to make Charles keep quiet, and so Charles had to stay after school."

Of course finally, at the end of the story, the author includes that Laurie's teacher tells his mother there is no Charles in kindergarten as a final clue that Laurie is in fact Charles.