In the middle of the night, 8-year-old aardvark Arthur Read and his 4-year-old sister, Dora Winifred “D.W.” Read, peek into a photo album and sees pictures of a younger Arthur without glasses. Not recognizing Arthur without them, D.W. believes that she and Arthur had another brother at one point. Arthur, however, clears this up by telling her that his parents, Mr. David Read and Mrs. Jane Read, gave them to him during the second grade (when D.W. was two years old) and why he started wearing glasses. In a flashback, Arthur is shown having trouble with his eyesight, which is why he later got glasses. When Arthur's schoolmates tease him for wearing the glasses, he tries to find ways to avoid wearing them, with disastrous results. But after finding out that Wilbur Rabbit, the actor who plays his favorite hero, Bionic Bunny, wears glasses, Arthur becomes more confident about his own glasses, and the teasing soon stops.

With school picture day coming up, Mary “Muffy” Crosswire decides to make her best friend, Francine Frensky, beautiful by giving her a dress and taking her to a beauty salon for a new hairstyle. Francine is mortified with her new hairstyle, gets teased at school for it, and is disallowed by Muffy to play in a kickball game to make sure she looks nice for her school pictures. Eventually having enough, Francine gets in the Kickball game and wins for her team, getting incredibly dirty afterwards. Despite still being filthy when taking her school photo, Francine likes it and even trades photos with Arthur, much to Muffy's chagrin.

It’s a new school year at Lakewood Elementary School, and Mr. Haney, the principal, is assigning every student their new classroom instructor. Arthur and his friends are horrified when they learn that their third-grade teacher will be the infamous Mr. Nigel Ratburn, who is rumored to be the toughest teacher in the entire school. Worse, predictor Prunella Deegan tells the gang false facts about Mr. Ratburn, like eating nails for breakfast without milk and sending children to death row if they get an answer wrong, making the kids even more afraid of Mr. Ratburn. After overhearing Mr. Ratburn requesting "boy's heads", Arthur and Buster believe that their teacher is trying to kill them, so they spy on him (along with Francine) to see if he does anything out of the ordinary. It eventually turns out that Mr. Ratburn is actually performing a puppet show, with the boy's head being the head of the puppet. Arthur and Buster are relieved to find out that Mr. Ratburn has a soft side, but they are still afraid of his tough teaching and heavy loads of homework.

Mr. Ratburn announces that Lakewood Elementary School is having a spelling bee, and all the students have their own strategies to prepare for it, except for Arthur, who only practices one word (aardvark) from a rap song. Fortunately for Arthur, aardvark happens to be the word that Mr. Ratburn asks him to spell, which he does correctly, being the only classmate, other than Alan “The Brain” Powers, to pass and advance to the school's Spellathon. In order to do better, Arthur does a lot more studying to improve his spelling, missing out on fun activities with his friends. At the day of the Spellathon, the Brain is eliminated from the competition after spelling the word "fear" incorrectly. Prunella who won the Spellathon last year, is also eliminated after spelling "preparation" incorrectly. Arthur, however, manages to spell the aforementioned word correctly and win the Spellathon.

D.W. develops a fear of octopuses while on a field trip to the aquarium with her class. At home, to mock D.W. for her fear, Arthur plays a cruel prank on her during her bath and is subsequently sent to his room. The next day, the Reads and Arthur’s best friend, Buster Baxter, go to the beach, but D.W., thinking that there might be octopuses in the lake, is too scared to swim and Arthur and Buster are forced to play with her on the sand, much to their embarrassment. However, after Arthur teases her by pretending to be under attack by an octopus, D.W. overcomes her fear and learns from the beach's lifeguard that octopuses are never found in lakes. At the end of the day, Mrs. Read promises that they will go back to the beach soon.

On a class trip to a state park, Buster, with Arthur’s help, finds a fossilized dinosaur footprint, but the former is dismayed at the rule that all fossils should be given to the museum and not be kept for the one who found it, so he hides the fossil in order to keep it, to Arthur's dismay. While trying to keep the fossil a secret from everyone, Buster realizes that the guilt of stealing is ruining his life and decides to give it to the museum. The museum curator suggests that the dinosaur who made the footprint may have been a baby Daspletosaurus or an adult Coelosaurus and Buster and Arthur are given the credit for finding it.

Arthur is jealous when D.W. creates an imaginary friend named “Nadine”. When the Reads and Buster plan to go to Wonder World, where a new ride called the "Hurl-a-Whirl" has opened, D.W. plans to take Nadine to the park, worrying Arthur and Buster, fearing that Nadine will embarrass them. They attempt to find ways to avoid Nadine from coming but fails. At the park, Arthur tries ignoring D.W. and Nadine, but D.W. says that Nadine wanted to give him extra tickets for rides, because she wants to be his friend, touching him and accepting D.W.'s imaginary friend.

Arthur is the first to borrow the new Scare-Your-Pants-Off book, The Mysterious Hand, from the Ellwood City Public Library, but he accidentally drops it on his way home. Suspecting his friends to have stolen the book, Arthur recruits Lakewood Elementary’s class bully, Shelley “Binky” Barnes, who seemingly doesn't like to read, to help interrogate the possible suspects, including Sue Ellen Armstrong, Francine, and Buster. When it turns out that no one has the book, Arthur is forced to pay for the missing book, but it turns out that Binky found it, being initially unaware of who it belonged to until it turned out that nobody else had Arthur's copy. After Arthur discovers that Binky likes reading books after all, the latter warns him not to tell anyone about it, as he is embarrassed to admit it.

Arthur starts his own pet-sitting business to prove he is responsible enough to get a dog of his own. He ends up getting much more pets to take care of than he bargained for, including his neighbor, Mrs. Wood's evil dog, Perky. When Perky goes missing on the day Mrs. Wood is picking her up, Arthur fears that he is not a good pet owner until he finds that Perky has given birth to a litter of puppies (which indirectly explains why Perky was acting so aggressive). As a reward for taking care of Perky, Arthur is allowed by Mrs. Wood to adopt one of her newborn puppies and pays D.W. the $10 he was given after he had promised to pay her for helping him.

After Arthur wishes D.W. would be more like him, D.W. decides to dress like Arthur, follow him around, and do the things he likes to do. While Arthur likes this at first, he is soon fed up, especially when his friends start excluding him because they do not want D.W. around. After D.W.'s own friends refuse to play with her due to her changed attitude, Arthur allows her to change back to her old self, though D.W. hints that it was all a set-up.

Francine is furious at Arthur for a joke he made at her expense, which becomes more of a problem to the other students (even D.W.) when Mr. Ratburn assigns the two to work together on a weekend project. The next day, they go to the library together in order to do research on their project but lose track of time, getting locked inside during closing time. Realizing that the library won't open again until Monday, Arthur and Francine try to find ways to escape separately. Arthur eventually becomes worried and aggressive for Francine's safety and tries to rescue her, which touches Francine when she finds out and they make up. Later, the Reads and the Frenskys soon come to rescue them, and the duo makes a report about the acts of heroism at school the next day, impressing Mr. Ratburn.

Arthur is in charge of helping Lakewood’s cafeteria lady, Mrs. Leah MacGrady, with a fundraiser, but when he tries to give the money he raised to her, she is distracted by a phone conversation, so Arthur leaves the money in the kitchen. However, the money mysteriously disappears, and Arthur is falsely accused of stealing it, which prevents him from going to a school picnic as his punishment. Buster, acting as a detective, tries to prove Arthur's innocence before the day of the picnic. When he seemingly fails to find any clues, Buster eventually deduces that Mrs. MacGrady had unknowingly put the quarters into brownie mix, clearing Arthur's name and allowing him to attend the event.

Arthur and his friends attend a sleep-away program at Camp Meadowcroak, where everything is a competition between girls and boys. When Meadowcroak's rival camp, Horsewater, plays a spooky prank on them, Arthur convinces everybody to work together in Meadowcroak’s annual scavenger hunt, and they manage to win.

Buster falls behind with his schoolwork, and is threatened with repeating third grade if he does not improve. Arthur, Muffy, and Francine tutor him, but he struggles to pay attention.

Following the events of "Arthur's Pet Business," Arthur is trying to train his new puppy, Pal Read, to behave, but Pal ends up making huge messes and causing disturbances around the house. Mr. and Mrs. Read try to sell Pal, making Arthur upset, but they change their minds.

Arthur wants Moon Boots and tries to get money to buy them. While Arthur is cleaning the garage, his neighbor, Mrs. Tibble, comes by and, mistaking it for a yard sale, offers to buy a necklace for the amount of money he needs for his Moon Boots. Arthur regrets this decision when he learns that the necklace is a present for Mrs. Read’s birthday, so he tries to earn it back.

Arthur thinks that babysitting is an easy job until D.W. volunteers him to babysit Mrs. Tibble’s two identical twin sons, Tommy Tibble and Timmy Tibble, with a bad reputation of being destructive and evil. After some initial struggles, Arthur gets the twins to behave by telling them a scary story.

Mr. and Mrs. Read are hosting their annual family reunion. Arthur tries to avoid his enemy cousin, Mo Read, who has bullied him during past reunions, while Mr. and Mrs. Read deal with their eccentric relatives. When a thunderstorm forces the Reads to spend the rest of the party indoors, Arthur learns that Mo has been looking for him to ask if he could give her a piano lesson.

Arthur and Muffy have their birthday parties on the same day and neither can postpone. While everyone is frozen with indecision over whose party to attend, Arthur and Francine then work together to merge the two parties into one everyone can enjoy.

Feeling sorry for Francine getting the challenging roles in all of Lakewood’s class plays, the whole class vouches for her to star as Thomas Edison in the next play. However, they regret their decision when Francine tries to take charge and is very aggressive, leading to heated disputes between her and the entire cast.

On baby Kate Read’s first birthday, D.W. reminds Arthur of when he was nervous after finding out Mrs. Read was pregnant. When Kate is born, Arthur is worried that she hates him, since she cries hysterically whenever he is nearby.

Following the events of the previous episode, D.W. feels jealous of the attention Kate is receiving from the rest of the family and tries everything to get rid of her, but nothing works.

Note: This episode is the same as “Arthur’s Baby”, but it’s on D.W.’s side.

When Arthur is assigned to write a story, he writes about how he got Pal (from "Arthur's Pet Business" and “Arthur’s New Puppy”). Afraid that people will find it boring, Arthur begins fictionalizing the events using advice from different people. Once he realizes how strange the story is, he changes it back and learns that the truth is still interesting.

It is Downtown Day in Elwood City and the Reads attend a festival. They pass a clown giving balloons and Kate is crying because she wants one. Nobody but Pal understands the crying Kate wanted a balloon, so Pal runs off to get a balloon for her, but Arthur thinks he is running away from him.

When D.W.'s pet bird, Spanky, dies, she leaves a can of flowers on his grave after his funeral, but finds a toad in it. The toad constantly follows D.W., but she is annoyed that it will not leave her alone. But when the toad disappears one morning, D.W. realizes that she misses it. Once they reunite, D.W. names the toad, “Toady”.

Arthur and Buster work on a project together, but Buster does not have the time for the project or for Arthur, instead talking about his new friend, Mike. When Buster keeps forgetting about him, Arthur decides to end his friendship with Buster, until he learns who Mike really is and Buster apologizes.

Arthur borrows a new computer game from the Brain, but Mrs. Read needs to use her computer for tax season. When Buster visits, Arthur shows him the game, but just as Arthur was about to win, he and Buster fight over the keyboard and accidentally knock it to the floor, causing the monitor to shut down permanently. They, with the Brain’s help, try to figure out what is wrong with Mrs. Read’s computer before she comes home.

While playing a game of Truth or Dare with Muffy, Francine recalls the time, back in second grade, they first met and became friends. Muffy lies about cheating on a test, causing Francine to be in detention for a week. When Francine is needed for a crucial softball game, and Muffy's lies finally catch up to her, she finally comes clean, allowing Francine to return to the game.

Arthur is down in the dumps that he misses his second chance to go to Camp Meadowcroak with Buster since he is going on a road trip with his family. The Reads face many mishaps such as their hotel reservation getting cancelled and it rains consistently until the last day of their trip. When Arthur gets back, he is lucky that Buster had an even worse trip than him.

Arthur and D.W. visit their Grandpa, Dave Read, who lives on an old, rundown farm. Grandpa Dave disagrees their help running it, but Arthur and D.W. are concerned by the state of things and try to help him fix up the farm with the help of his friends.

Arthur is determined to win a year's supply of his favorite breakfast cereal, Crunch, by composing a jingle, but he cannot come up with any ideas. He hears D.W. singing a song about Nadine and copies it. Arthur feels guilty, so he mails the song with D.W.'s name instead of his, and it wins the contest, much to D.W.'s confusion.

D.W. is jealous of Emily Leduc’s performance in their gymnastics class and is determined to become better than her, which endangers her when she climbs on a high balance beam and nearly injures herself. Afterwards, D.W. and Emily apologize to one another and become friends.

Annoyed by Francine's attitude, Muffy bets that she can’t be nice for a week. Noticing how straining the bet is on Francine, Arthur, Buster, and the Brain try to get her to lose her temper, but Francine manages to keep it under control until the bet is over.

When Arthur and Buster are forced to eat lunch with Binky's gang, the Tough Customers, they tell Arthur they think he has never "gleeped" anything, but to impress them, he tells them he has, only to find out later that "gleep" is slang for "steal." Rumors spread about Arthur being a thief, while Binky's gang pressures him into their ranks.

Arthur is looking forward to his family trip to the Elwood City Circus, but he gets an unsettling case of the chicken pox, and is unsure if he will get better in time for the event. When his Grandma, Thora Read, visits to take care of Arthur, D.W. gets jealous of the attention he gets and tries to pretend she has it too.

Arthur is upset when Pal has to stay at the vet’s office overnight for being sick. He blames D.W. for this, but when the vet tells him that Pal has been eating too much human food, he has to apologize to D.W. and learn what Pal is and isn’t supposed to eat.

D.W. gets a new two-wheel bike for a bike-riding fundraiser after the Tibble twins tease her for her tricycle. She tries to learn to ride it with Arthur's assistance. After several injuries and failed attempts, D.W. gets the hang of riding her bike.

Arthur and his friends try out for the baseball team, and Arthur struggles with catching the ball while Francine is unable to throw accurately. When Francine wishes for her father, Oliver Frensky, to kick Arthur off the team, thinking he is the reason for the team not doing well, he makes Arthur and Francine coach each other to get better.

Arthur and his friends are assigned to write about what they do over the weekend, but the rain ruins their plans. Arthur and D.W. bother each other and are sent to Grandma Thora's, where she shows them old home movies and comic books that give Arthur a great idea for his assignment.

Grandma Thora is oblivious to the fact that she is a poor cook, and when she bakes cookies for a school bake sale, Arthur and D.W. try to stop her bad cooking from ruining the bake sale without hurting her feelings.

Rumors circulate about Sue Ellen and her family, who have just moved into the neighborhood. Buster jumps to the false conclusion that they are aliens and tries to expose them, but everyone else learns about how Sue Ellen traveled the world and change their opinions of her.

The Brain spends the weekend with the Reads while his parents visit an ice cream convention. The Brain is neat as two pins, finishes his homework early, and reads to D.W., making Arthur feel under the weather for them. When the Brain invites Arthur over to his house, Arthur learns that he is messy and is just acting polite because he is a guest.

D.W. keeps a snowball in the freezer from "the best day of her life," but it disappears the next day and D.W. is mortified. Buster and Francine investigate, listening to biased accounts of those present the day the snowball was gone. After several arguments and accusations, D.W. lets the incident go as the first snowfall of the year appears.

Arthur, Buster, and Francine are assigned to do a group project on Ancient Rome. They separately work on a comic book, which ends up being inconsistent and not working due to disagreements. They learn that they have to work together to make a good project.

Binky nefariously teases Sue Ellen, who demands that he apologize. When he does not, she challenges him to a fight to settle it. He is nervous about it, especially when he finds out she knows Tae Kwon Do, and tries to beat her in music instead. When Sue Ellen is better than him in that as well, Binky accepts that Sue Ellen is tougher than him.

For her half-birthday, Prunella's older sister, Rubella Deegan, gives her a cootie catcher. Rubella claims that it can tell the future and the answers it gives do come true. Arthur and his friends begin following the advice of the cootie catcher. When the catcher is ruined, they realize that they should not let it control their lives.

Arthur has a loose tooth, but he is the only one in his class that has not lost any of his baby teeth yet. He tries to pull it out to get Francine to quit teasing him, but nothing works. So Arthur learns that people lose their baby teeth at different ages and tells Francine, only for her to accidentally hit him with a ball and finally knock out his tooth.

D.W. wants earrings because Emily has them. Mrs. Read then takes her shopping for earrings the next day, and while at the superstore, they run into Muffy's father, Edward “Ed” Crosswire, who needs to speak with Mrs. Read. All fed up, D.W. wanders off and gets lost in the store. While trying to find her way back, she runs into Emily and sees her earrings have turned her ears green. Upon returning to Mrs. Read, D.W. changes her mind about wanting earrings.

D.W. wants to help out at Aunt Lucy Read’s wedding, but she is too little. Arthur is the ring bearer and their rude cousin, Cora Read, is the flower girl. During the wedding, Cora aggressively distracts Arthur, causing him to accidentally throw Aunt Lucy’s ring into the organ pipes. Arthur is too big to crawl into the organ and Cora does not want to get dirty. So D.W. volunteers and successfully retrieves the ring. As a reward, Aunt Lucy allows D.W. to be both the ring bearer and flower girl.

When Arthur complains about the state of the park, his father starts a brigade for Arthur and his friends to clean it. Arthur's friends are enraged at him for starting the brigade, despite him trying to explain that it was his father's idea, not his. As a result, Arthur has to do the job himself with only Francine's father advising him. However, the next day, Arthur stands up to Binky and his gang when they tease him and orders them to help him clean the park. Arthur's friends decide to help him after overhearing the incident with Binky's gang.

Mr. Ratburn's class goes on field trips to several of the students' parents at work to learn about careers. Francine is embarrassed by Oliver’s job as a garbage man and tries to cover it up by informing her friends that he is in a secret organization and just pretends to be a garbage man for cover. However, Francine eventually decides to admit that Oliver is really a garbage man when everyone sees that he built a playground out of things he found at the dump.

Muffy is allergic to the new carpet in her house, so she stays with Francine while the carpeting is being removed. During Muffy's stay, Francine is unable to handle Muffy's spoiled feelings, and Muffy can’t deal with the less-than-wealthy condition in which the other Frenskys live.

D.W. loses her favorite blanket, so she enlists Arthur’s help to search for it, retracing her steps over the entire Elwood City. D.W. is upset when none of the businesses have her blanket, but when she struggles to sleep without it, Mrs. Read hands it over to D.W., telling her that she washed it.

Mr. Ratburn loses his voice and his sister, Ms. Rodentia Ratburn, substitutes for him. She is a kindergarten teacher, and although the class is glad to have some easy work at first, they soon get bored and they realize they miss Mr. Ratburn's tougher classes, so a cured Mr. Ratburn returns early from his week off.

Fern Walters, who wants to be a poet, is the only one in class to enter a poetry contest, which is to be judged by famous poet Jack Prelutsky. The others think poetry is uncool, and start making fun of her. Fern bets them if they cannot write and submit their own poems, they must join the poetry club for a year. In doing so, Fern's friends find writing poetry fun.
Guest star: Jack Prelutsky as himself.

When their favorite series of books is banned from the library by a parental organization who believe scary books are mature for children, Arthur and his friends get together a petition to get them back — all except Muffy that is, as it turns out that Mr. and Mrs. Crosswire are the founders of the parental group. Everyone gets a surprise when the books' author arrives to defend her books, and she happens to be Ed’s former teacher.

Arthur and his friends create a club to exclude D.W., but neither can agree on the rules. Everyone starts creating their own clubs with strange rules, alienating those who want to join.

Francine's bike is too small for her, so Oliver finds his old bike, except she is embarrassed by the fact that it is old and rusty. When her friends tease her about the bike, she hides it and pretends it is stolen. The bike then gets thrown out, and when Oliver finds it, broken, they work together on fixing it up.

Arthur has his first sleepover with Buster and the Brain, even with all the talk of UFOs. D.W. wants to join them so that she can take a picture of a UFO. But the trio keeps declining her, so D.W. plays a prank on them with a flashlight in retaliation, and payback strikes when they surprise her with a fake alien, then tricking her into spotting a fake UFO.

Arthur has never stayed up until midnight on New Year's Eve. His friends all have different claims on what happens at midnight, so Arthur tries to stay up until New Year's Eve to find out what occurs. He is disappointed when he sleeps through it, although Grandma Thora reassures him that the following year will be exciting.