The main characters on "The Magic School Bus" include the teacher, Ms. Frizzle, and the kids in her classroom. Kids who appeared in every episode included Carlos, Keesha, Dorothy Ann, Phoebe, Wanda, Ralphie, Arnold and Tim. Liz, Ms. Frizzle's pet lizard, also appeared in every episode.
Most of the main characters had specific lines that were considered to be their catchphrases. Some of the most famous are Arnold's "I knew I should have stayed home today!"; Ms. Frizzle's "Take chances. Make mistakes. And get messy!"; and Wanda's "What are we gonna do? What are we gonna do? What are we gonna do?"