"Shows and Tells" is the sixth episode of season three and the thirty-second episode overall of the animated children's series The Magic School Bus. It originally aired on October 19th, 1996.
It's the International Show-and-Tell Competition and Arnold and Dorothy Ann are representing Ms. Frizzle's class. Arnold brings a webbed hoop, left behind by his great-aunt Arizona Joan, the famous archaeologist, but he has no idea what it is. Using clues from it and Joan's journal, the class makes educated guesses about its uses. To test their hypotheses, Ms. Frizzle turns the bus into a "Supposatron," a magical device designed to evaluate guesses.
At the International Show-and-Tell Competition, the class is waiting to get on and Dorothy Ann is ready for her show-and-tell performance with Arnold, who has yet to show up. Tom and Ella show up with their large pumpkin and the rest of the class panics over Arnold's absence. Arnold shows up just in time and tells the class that he left his rock collection at home. He, instead, brought a webbed hoop. Since no one (not even Arnold) knows what it is, Ms. Frizzle arrives just in time for the class to tell her about it. When Arnold tells her that it was left behind in his attic in a trunk by his late great-aunt Arizona Joan, the famous archaeologist (who has told Arnold stories about how she searched for things left behind by people a long time ago and how she tried to figure out how people lived based on the stuff she found when he was little, calling her entire life a voyage of discovery according to his mother), he shows his great-aunt's journal, which prompts Ms. Frizzle to take the class on a field trip, leaving Arnold behind to watch the two-way Show and Tell-evision to show him where the class is and what they are doing.
As the class run to the bus, Ms. Frizzle explains to the class the "art-a-fact", which is anything made by paper who lived a long time ago and gives one clues to how people live their own lives. Ms. Frizzle also adds that scientists guess what a certain object is and put clues together to do so, called a hypothesis. So Ralphie uses his intuition to surmise what the webbed hoop is and states that it could be a sort of shield. Tim, however, says it looks more like a net. Ms. Frizzle uses the bus to transform and to the class' surprise, the bus remains the same as it usually is. They follow Ms. Frizzle inside the bus to find that the inside of the bus changed rather than its outside, which Ms. Frizzle calls the "Suppose-a-tron", the guess tester. The teacher makes a duplicate of the webbed hoop: one to test and the other to give back to Arnold. D.A. surmises that the object was made a long time ago according to Arizona Joan's journal and that she found it 14 miles northwest in Fort Walkerville, which is outside of town. The class knows that the hoop is made of wood, meaning there were trees in the town, and that in Joan's journal, hunters and farmers were present in the town. In order to find out how they would know whether the guests are right or not, the class takes a trip through a projector screen in a "what if?" world. They come across a group of tribal people the class supposed and used their bow and arrows to attempt to attack the class, who take cover behind the trees. Ralphie uses the hoop as a shield, which proves to be futile since the arrows go right through it.
Back at the show-and-tell show, Liz gives Arnold the hoop back and meanwhile, the rest of the class exit the "what if?" world through the screen inside the "Suppose-a-tron" inside the bus. They finally come to a conclusion that the hoop isn't used as a shield after all and Arnold calls through the Sow and Tell-evision to warn the class that he and D.A. go onstage any minute. Wanda then reads in the journal that Joan wrote evidence of a canoe where she found the hoop. Tim surmises that the hoop is used as a fishing net and Ms. Frizzle tests the hypothesis on the screen once again. The class hop inside the screen and row through the river on a canoe. Tim attempts to use the hoop as a fishing net, but the big fish circumvents the hoop and the small ones swim right through. So Tim finally concludes that it isn't a fishing net after all. The class then comes across the turbulence of the river and at the show-and-tell show, Arnold is waiting impatiently for the rest of the class to return as he views them through the Show and Tell-evision.
The class has made it back inside the Suppose-a-tron soaking wet and Keesha tells the rest of the class that the hoop wouldn't have so much beautiful colors if someone was going to stick the hoop into the water. She surmises that the hoop is a hat and D.A. reads in Joan's journal that she found shells and beads people used to decorate their clothing for ceremonies. So Ms. Frizzle activates the screen and adds in dancers and drums as D.A. guesses that it is a harvest ceremony. So Ms. Frizzle also adds in fields, corn, and changes the time of day to night. So the class hop inside the screen to join the harvest ceremony and Keesha sees that the hat can't stay on her head and that there is nothing to keep it on her head as well. So she acknowledges that her hypothesis is erroneous.
During the show-and-tell show, Arnold is still waiting for the rest of the class to return, for he is about to present on the show in five minutes. The rest of the class return to the Suppose-a-tron and the class is running out of clues. So D.A. contacts Arnold through the Show and Tell-evision to ask if he has anything else he could tell the class. Arnold then finds arrows inside his bag and the class discern the arrows and the hoop, learning that the two are decorated the same way, meaning that they complement each other. D.A. runs out of the Suppose-a-tron and back in the show-and-tell to obtain one of the arrows from Arnold and leave again, much to Arnold's dismay.
Arnold panics as he is up next and reluctantly walks onstage with his hoop. As Arnold is about to present, the rest of the class makes copies of the hoop and arrows and garners a bunch of the people Ms. Frizzle made up on the screen. The class hop inside the screen and D.A. implements a hoop and arrows competition. When the class learns that the hoops and arrows have matching colors and guesses what's round, has different colors, and goes with something pointy, they finally surmise that the hoop is an old dartboard that comes with arrows as darts to play it as a game.
At the show-and-tell, Arnold tells the audience that they have to use their intuition and hypothesis to guess what the hoop he is holding in his hand is and delineates what it is to have them guessing. When Liz throws one of the arrows through the hoop, Arnold finally comes to a conclusion to what the hoop is and elucidates to the audience of its use of a game being played a long time ago and tells them that it takes archaeologists to fit the clues together to learn what it is. D.A. arrives just in time to see that Arnold has won the award for his performance, and the latter shares his trophy with the rest of the class.
- This is the only episode in which the Bus never changed from the outside (even though it changed from the inside).