Wayside School is a thirty-story building with one classroom on each floor. Mrs. Jewls's class occupies the thirtieth floor, requiring students to race up all thirty flights each morning. The school operates according to its own absurd logic, with bizarre bells, eccentric teachers, and everyday events that defy normal expectations.
The story opens with Todd, a student in Mrs. Jewls's class, arriving a moment late and writing his name under DISCIPLINE on the blackboard. Homework piles up and Mrs. Jewls announces the Ultimate Test, a three-day exam that could send failing students back to kindergarten. Then a mysterious bell rings for only the second time in the school's history: the Erase-the-Blackboard bell. All teachers must erase everything, and Todd's discipline mark, homework, and the test vanish. In the basement, three mysterious men pack a silver ball and a gold Ping-Pong paddle into a black attaché case.
Mrs. Jewls decides the class should collect a million of something small to understand how large a million truly is. When Terrence, a boy who compulsively kicks things, clips his sore toenail in class, Mrs. Jewls seizes the clipping and declares it "one" toward their goal. The nail clipping collection becomes a running project, with tallies tracked on the blackboard.
D.J., one of Mrs. Jewls's students, develops hiccups that sound like "Up!" Kathy, the meanest girl in class, reflexively replies "Down!" each time, not realizing she is arguing with a hiccup. Mrs. Jewls sends D.J. to Dr. Pickell, the school counselor known as Dr. Pickle, who cures the hiccups by scaring D.J. Dr. Pickle then diagnoses Kathy with "oppositosis," a compulsion to say the opposite, and hypnotizes her, guiding her to imagine walking through a mirror. Kathy wakes up suddenly polite and kind, though her homework is now written entirely backward.
The three Erics in Mrs. Jewls's class compete to bring in the most nail clippings. Eric Fry, the athletic one, brings forty. Eric Bacon, the clever one, brings 349 by canvassing neighbors. Eric Ovens, the kind and perpetually overlooked one, has eighty-three but cannot get a word in. The now-kind Kathy lifts his arm and announces his contribution, and the class cheers.
A giant closet wrapped in chains and warning signs appears outside the classroom. Mrs. Jewls orders the children away and insists it is "not there." During a science lesson on the roof, a student named Benjamin points to a dark cloud in the distance. Mrs. Jewls gasps, rushes everyone inside, and identifies it as a Cloud of Doom. The room darkens.
The Cloud of Doom settles over the school for weeks. Louis, the yard teacher, watches a ball explode under the cloud's shadow. Walking home with Mr. Kidswatter, the principal, Louis suggests letting a student ring the giant iron gong that ends each school day. When Mr. Kidswatter learns that Louis has written books about Wayside School, he demands a chapter called "The Best Principal Ever!!!" Louis tells him he must first do something to deserve the title.
The cloud causes strange effects. A gust of wind tears student Sharie's umbrella from her hands and carries it skyward. Dana, a classmate whose talent is making funny faces, makes her "Doofus Face" and it freezes in place. Mr. Kidswatter engages Dana in a staring contest, and when he turns away, Dana's face returns to normal but his becomes stuck. He visits Dr. Pickle, who hypnotizes him. Mr. Kidswatter's face snaps back, but the expression transfers to Dr. Pickle. Dr. Pickle later tries to cure himself using the pickle stone and a mirror, but when he wakes, the Doofus face is trapped in the mirror. He smashes the mirror with his bronze bust of Sigmund Freud, and Kathy immediately reverts to her old argumentative self; the destruction of the mirror undoes the hypnotic treatment.
Under the cloud's influence, students grow irritable and begin blaming it for everything. Classmate Joy blames it for her failing arithmetic grade. Paul, another student, blames it for pulling classmate Leslie's pigtails. Mrs. Jewls snaps, doubles all homework, and announces the Ultimate Test will start Monday, then admits she herself is blaming the cloud for her harshness.
Mr. Kidswatter visits the classroom seeking a student to bang the gong. He means to select Dana but she bends down to scratch a mosquito bite, and Stephen, sitting behind her, is chosen instead. Stephen is terrified; he cannot do a single push-up. Louis coaches him, and classmates repeatedly tell him to "breathe." On Friday, classmates Jason and Rondi physically lift Stephen from his chair. On the stairs, he steps over a skateboard he had been dreading, and his fears vanish. He swings the mallet and misses the gong entirely, but the momentum spins him around and it strikes dead center on the second revolution. Stephen shakes Mr. Kidswatter's hand, the only student ever to do so.
The Ultimate Test spans three days. The Unbreakables, a four-student friendship group of Maurecia, Joy, Deedee, and Ron, each bring unique talents. On day one, a spelling bee narrows to Ron and Maurecia. When Mrs. Jewls switches to invented words, Ron misspells "whummph," and Maurecia wins. On day two, Jump Rope Arithmetic has students answer math problems while jumping rope. Joy breaks one hundred points but trips at 101. Maurecia jumps steadily for nearly an hour, earning 211 points. On day three, the Stairway Quiz sends students racing upstairs answering questions. Deedee leads but misses a question about three-toed sloths, which have twelve toes total. Maurecia wins the overall test. Despite Joy's jealousy, the Unbreakables reunite at the flagpole and shout "Unbreakable!"
Nobody is sent to kindergarten; Mrs. Jewls designed the test so each student could shine. Classmate Myron brings thirty-seven nail clippings, pushing the total to 999,999. Then a bell nobody has heard before sounds: a kachooga followed by one, then two, then three boops. Mrs. Jewls reads that this sequence means a Cloud of Doom is about to destroy everything. Explosions shake the school and the lights go out. The children try to flee, but the closet, revealed to be full of paper clips, has toppled and blocked the door. Stephen's training helps them force it open. Mrs. Jewls leads the class down the dark staircase. Someone trips on a skateboard, sending everyone sprawling. A door opens, and a teacher with a long fingernail beckons them inside.
The teacher is Miss Zarves, who occupies the supposedly nonexistent nineteenth floor. She conducts a bizarre history review about obscure, non-famous people and assigns stacks of papers, some written in Chinese. After an indeterminate stretch of time, Myron offers to trim Miss Zarves's long pinky fingernail. The moment he clips it, he finds himself standing on the staircase with his classmates. He holds the clipping aloft and shouts, "A million!"
The storm has passed. The school's interior is in disarray, with furniture shuffled across all thirty floors, and the 999,999 other clippings are scattered and lost. The sun shines, birds return, and the sky is blue. Louis shovels snow off the roof and discovers Sharie's umbrella buried in a drift. He yanks it free but slips off the edge, hooking the handle on the flagpole and spiraling safely to the ground.
To celebrate, Miss Mush, the lunch lady, creates "rainbow stew," choosing ingredients by color: red cabbage, unpeeled bananas for yellow, pumpkins for orange, and her assistant Mr. Pepperadder's shoes for black. The stew looks like lumpy mud, and Miss Mush apologizes as she serves it. When the children taste it, however, they discover they can taste colors. Everyone declares it the best lunch ever. Miss Mush whispers that there is no recipe, because no two rainbows are the same. Everybody chews.