When Rivals Came to Roost

Synopsis
Lakewood Elementary students must share their school with rival students whose classroom gets flooded.

Plot
Brain gives a presentation on the history of Lakewood Elementary's rivalry with Mighty Mountain: Lakewood lost in a hula hoop contest, sports, spelling bees, quilting bees, and competitive beekeeping. Brain then talks about the science fair, insisting that Lakewood will win this year.

When Rivals Came to Roost

As Muffy is disgusted by the class's science project on worms, Mr. Ratburn announces that a pipe in Mighty Mountain's third grade classroom has burst, and his class will be sharing their room with Mighty Mountain students because their classroom got flooded. Brain is worried that Mighty Mountain will find out about their science project, and Mr. Ratburn says that he will get to see theirs, too.

While eating lunch outside, Ladonna gives everyone pins of Mighty Mountain's school colors, and Arthur, Baxter, and Muffy discuss ways to make the students feel welcome. Brain still considers Mighty Mountain a rival, and does not want to welcome them.

When the class moves in, Los Dedos makes an agreement with Brain that the science fair will be about "good science, not competition." She shows him what was salvaged of her science project: a bunch of ants in a pickle jar. He is disappointed and doesn't believe that the class used to have a big display. She opens a can of soda, which sprays all over his project.

At Arthur's house with Ladonna, Arthur, Muffy, and Brain, Buster explains that ants and worms are "mortal enemies." He describes a Bionic Bunny comic, but Brain and Arthur bicker that Bionic Bunny isn't scientific and that the worms and ants are in separate containers.

Arthur, Buster, Muffy, Ladonna, and Brain are annoyed by Mighty Mountain due to them going first at lunch, using the four square court, and sharpening their pencils first. When Buster notices that Danny and Los Dedos are gone during lunch, they run to the classroom and find that the worm container has been smashed. Danny and Los Dedos claim that it was an accident, and the kids are forced to combine their science projects and put the worms and ants in the same container.

Danny and Los Dedos feel that they aren't trusted and plan to help with the science project by getting something to "move worms," which is back at Mighty Mountain. Muffy and Brain overhear this and chase them to the school. There, the "moving worms" tool is revealed to be a pair of soft tongs, and the classroom is still too damaged to enter. Brain feels bad and apologizes to Los Dedos, who explains that that is just her chess nickname and her real name is Isabella. Buster runs in to say that the ants and worms are "attacking" each other, and they run off to make a check on them.

Brain and Isabella observe that the ants and worms are working together to distribute nutrients, and combine their projects into a "Worm and Ant Compost Hotel." At the science fair, the judges award the prize to Lakewood Elementary and Mighty Mountain.

Major

 * Brain
 * Los Dedos
 * Ladonna Compson
 * Buster Baxter
 * Arthur Read

Minor

 * Mr. Ratburn
 * Danny Torres
 * Squirm
 * Antic
 * Antic's aunt
 * Bionic Bunny
 * Mr. Wiggles
 * Leah MacGrady

Cameo

 * Biff Biffington
 * Debbie
 * Maria Pappas
 * Jenna Morgan
 * Binky Barnes
 * Francine Frensky
 * George Lundgren
 * Leah MacGrady
 * Steve Pappas
 * Otis
 * Sue Ellen Armstrong
 * Cecilia Tingley
 * Kiefer
 * Trevor Brown
 * Kenny
 * Portia Demwiddy
 * 3rd Grade Male Cat
 * 3rd Grade Female Aardvark

Episode connections

 * This episode is similar to "April 9th," where Arthur and his schoolmates are temporarily transferred to Mighty Mountain Elementary School after a fire breaks out at Lakewood Elementary School.
 * Buster holds up a bag of jelly beans from Patrick's Chocolates.
 * The events of "Brain's Chess Mess" are mentioned to have happened "a few months ago."