How does the change in Laurie's clothing on his first day of school signal a change his behavior?

The change
in Laurie's clothing is described in the first paragraph of 's short story, "." It
foreshadows the behavioral changes in Laurie, as manifested through the character Charles, whom
Laurie invents. 

Here is the paragraph: 

The day my son Laurie started kindergarten he renounced corduroy overalls with bibs and
began wearing blue jeans with a belt; I watched him go off the first morning with the older girl
next door, seeing clearly that an era of my life was ended, my sweet-voiced nursery-school tot
replaced by a longtrousered, swaggering character who forgot to stop at the corner and wave
good-bye to me.

Jackson's word choice and description of
Laurie's new attire foreshadow the behavioral changes to come. First, she uses the word
"renounced." Synonyms for this word include shun, reject, and disown. This shows that
Laurie is asserting his independence with his clothing choice. One can infer that his mother
made the clothing choices up to that point. Now Laurie is casting aside the clothing he used to
wear and choosing blue jeans with a belt, a more grown-up choice. His mother, the narrator,
describes him as "swaggering," which suggests Laurie feels more grown up and
impressive in his new attire.  

The mother describes watching her
sweet-voiced preschooler being replaced by a child who swaggers. He also wears clothing that
shows he is leaving behind a part of his childhood. He even forgets to turn around and wave to
his mother, showing that he doesn't think he needs her as much as he did
previously.