"Gets Ready, Set, Dough" is the ninth episode of season one of the animated children's series The Magic School Bus. It originally aired on November 5th, 1994.
Ms. Frizzle is fixing the bus and it capriciously malfunctions. Inside the classroom, the class rehearse for a surprise party to throw her for her birthday. When Arnold feels that something is missing, Dorothy Ann remembers her chemistry experiment and mixes water, sand, and cement to "get something new", which is cement. They then realize that they forgot the cake and cancel the surprise. A gloomy Ms. Frizzle walks in and informs them that the field trip is canceled due to the bus' malfunctions. It was going to be to a bakery to learn about chemistry and Carlos decides to convince her to continue it, prompting her to schedule it regardless of the bus issues.
As the bus rides through the city streets, it shrinks down to size. But Ms. Frizzle doesn't let that stop the field trip. She accelerates it through the mail slot inside the bakery, which an Italian baker is working. The bus sprouts wings and flies over the baked goods. Carlos suggests that they should make their own cake, but they have to do it while inconspicuous from Ms. Frizzle's eye, for they want it to be a surprise for her. So he convinces her to go to the auto parts shop next door and she puts Liz in charge before leaving.
Liz rides the bus and flies into the kitchen, where the baker catches it and mistakes it for a moth. He swats at it with a fly swatter and it disappears behind a couple of jars before transforming into a normal mini-sized bus. As the chef leaves, the class reads the cookbook for the cake recipe. Carlos orders Ralphie to get two eggs, Tim and Wanda sugar and flour, Liz salt and cream of tarter, Keesha milk, Phoebe butter, Arnold baking soda, and Dorothy Ann the mixer. They get to work and Carlos runs off to get the chocolate.
The class grabs all the ingredients for the cake and Ms. Frizzle returns to see how they are doing on their work. Dorothy Ann, who learned that baking soda mixed with water makes vinegar, distracts her and asks for her help with an experiment. While the others work on making the cake, the bus once again shrinks down to size in an arbitrary manner, shrinking them even smaller than they were before.
Carlos leaves after telling the class he has another idea. While he is away, they find cubes of salt and diamonds of sugar. They learn that minerals look much different when looked at in a much smaller perspective. Meanwhile, Carlos has used the spoon as a catapult and flings salt into the bowl. The class enters the bus and adds the flour and sugar. They eventually learn that flour, when viewed close up, is made of different parts as well. When they mix it into the chocolate, they learn how the colors change and that they could still see which of the bits are chocolate. Little do they know, the baker is watching and is convinced that the bus is a bug flying inside the kitchen. So he contacts the Smug Bug Pest Control via telephone.
As the bus continues to add the ingredients, it unwillingly flies to Ms. Frizzle, who is still focused on Dorothy Ann's experiment. So Dorothy Ann distracts her again and shows her what happens when a bunch of baking soda with a sparse amount of water inside, which causes it to overflow inside the bottle. So Dorothy Ann puts a balloon on top of it and Ms. Frizzle tells her that baking soda and vinegar makes a gas that pushes the balloon out, which is tantamount to filling a tire with air. Ms. Frizzle then concludes that the bus needs new tires and goes to the auto parts shop to find out the price of new ones.
Meanwhile, it is revealed that the Smug Bug Pest Control thinks that the baker is crazy, prompting him to do the work himself. While the bus mixes all the ingredients together in the bowl, the class learns that air is getting beat into the mixture and all the ingredients coalesce to create one new thing, which is cake batter.
The class then learns that cooks and chemists are alike: both measure out ingredients and mix them together to make something new, the only difference being the cook gets to taste his/hers. When the baker comes back into the kitchen, the bus drops into the cake batter. The baker notices the bowl of batter and pours it into a cake pan. He puts it into the oven, baking the cake, much to the class' horror as they are getting baked along with it.
While the class is getting baked inside the cake, they notice a person dressed in white approaching the bus, who enters and turns out to be Ms. Frizzle, who reminds Liz of the heat shield. So Liz turns it on and the class feels much relieved. Dorothy Ann explains that the baking soda is making bubbles around the batter. When they hear a steaming sound, Ms. Frizzle explains that the water in the batter is vaporizing, thus expanding the bubbles and making them warmer. Just then, the batter solidifies, and the class learns that the cake is done. A pessimistic Arnold fears that they will get eaten along with it. Ms. Frizzle pushes a button on the dashboard, and the bus quickly breaks down. Dorothy Ann has a solution and decides to use baking soda and vinegar to create the gas pressure to push it out of the cake.
So just as the baker finally takes the cake out of the oven, the class uses the vinegar mixture to propel the bus out of it and back to the classroom, where they finally throw Ms. Frizzle the surprise party and offer her a cake the baker gave them. Arnold cuts her a slice with a bus shaped hole, and she states that "chemistry is a piece of cake", evoking laughter from the class.
- The TV tie-in book was called "Gets Baked in a Cake."
- Veteran film and television comedian Dom DeLuise voiced the baker.
- This is the first of a few times a child who saw the show appeared in person.
- Ralphie and Carlos mention two Wizard of Oz characters.