Doug discovers that though being Harry's best friend in Miss Mackle's second grade class isn't always easy, as Harry likes to do horrible things, it is often a lot of fun.

Follows the school activities of second-graders, Harry and Doug, as they participate in a secret mission to celebrate "Charlotte's Web," learn how to make green slime, and put on a skit warning about the dangers of smoking.

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.

When Sid, his annoying third-grade classmate, ruins Song Lee's origami praying mantis, Horrible Harry plots triple revenge on the troublemaker.

Horrible Harry, the class clown of Room 2B, returns to the spotlight with the Purple People, mysterious beings that only he can see.

Horrible Harry of classroom 2B cuts back on his mischievous pranks after falling for Song Lee.

Marvin thinks that the new girl in class, Lucy Tinker, is a liar and a thief, but then he finds that he may have misjudged her.

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.

Song Lee is upset when she receives hateful notes in class, but she finds an appropriate and positive way to deal with them.

A second grader is so embarrassed about her stuttering that she almost misses a chance to have lunch with her favorite author who has come to speak at school.