It's almost summer vacation and the students in room 2B are having trouble concentrating on their butterfly project, until a frightening-looking new teacher comes to supervise the Suspension Room and Harry is sent there as punishment for unruly behavior.
Spring becomes a memorable time for Miss Mackle's second-grade classroom because of the antics of Horrible Harry and the special insights of shy Song Lee.
When his friend Doug is infested with head lice and Mary convinces everyone to stay away, Harry and his other friend Song Lee stand by Doug and declare war on the bugs.
Selected to join the school safety patrol squad, third-grader Mary quickly turns into a bully, and classmate Doug suspects she may be tampering with the book raffle.
"When his best friend Doug discovers his top-secret hideout, Harry enlists his friends' help to save it from being developed into an apartment building"--
Spurred on by the promise of a mystery prize, Harry and Doug are determined to win the most points on Field Day, but Harry's sneaky tactics annoy their competition, making the two boys targets for revenge.
Miss Mackle's third graders share December holiday traditions--Christmas, Hanukkah, Kwanzaa, Three Kings Day, and Korean New Year--with each other and with Harry's great grandfather, who just moved to a nursing home.
When the origami pig that Song Lee made for her grandmother is seized by a substitute teacher, the usually well-behaved third-grader breaks a classroom rule to rescue it from the "June box."