Only thing I remember:
the main character, in 1st or 2nd grade, is the narrator and repeatedly mentions how proud he is to be “learning short vowels.”
At some point in the book, he puts trash into a mail box and a police officer yells at him.
The boy tearfully explains that he isn’t actually good at short vowels, so he can’t tell the difference between “letters” and “litters,” which is why he put his litter in the mail.
Ring any bells?