Arnold accidentally knocks out a bully named Harold during a baseball game, and Harold gives Arnold 24 hours to live before he beats him to a pulp.

"6th Grade Girls": Sixth grade girls Connie and Maria invite Arnold and Gerald to their school dance, but little do they know that Connie and Maria are using them to make their boyfriends jealous.
"The Baseball": Arnold's baseball idol, Mickey Kaline, is about to retire, so Arnold and Gerald go to Mickey's final game.

"Spelling Bee": Arnold competes in a Tri-City spelling bee to win money for a keyboard, but faces competition against Helga, who is being pushed by her father to win so she can follow in her sister's footsteps.
"Pigeon Man": Arnold confronts a man that has known and trusted pigeons all his life after Arnold's pigeon gets sick. The man has not been around other humans for many years, as he feels he cannot trust them. When Arnold takes him for a day in the city, Harold and his friends come along and accidentally destroy Pigeon Man's bird cages trying to make simple mischief.

"Save the Tree": Arnold and the gang must stop Big Bob from chopping down the oldest tree in town.
"New Teacher": When the kids make their new teacher, Mr. Simmons, quit his job, the replacement makes them realize what they lost.

"Helga's Love Potion": Helga drinks a potion to lose all of her feelings for Arnold.
"Gerald's Secret": Gerald's secret is revealed; he does not know how to ride a bike, so Arnold tries to teach him how.

"The Big Scoop": Arnold and Gerald compete against Helga in the school newspaper, but they find out that Helga is adding fake information for her newspaper. When one story begins to frighten all the students, Arnold and Gerald do some investigating, and print the truth-exposing Helga's fabrications.
"Harold's Kitty": Arnold and Harold rescue what they believe to be a stray kitten from the trashcan. As Arnold hangs up flyers, the mean and tough Harold forms a bond with the kitten, who ends up belonging to a grumpy old lady, Mrs. Ryle. When Harold refuses to give up the kitten, who he has named Cupcake, the police, Mrs. Ryle, and Harold's parents show up to take it back as Harold barricades himself in the house with the kitten.

"Longest Monday": Schoolyard tradition has it that on the first Monday of June each year, the fifth graders throw the fourth graders into trash cans. So, Arnold and Gerald try to make a run for it. As more people are thrown into trash cans and the fifth graders know all the routes, Arnold and Gerald find out eluding the fifth graders is harder that they thought.
"Eugene's Pet": After Arnold accidentally kills Eugene's fish with a yo-yo, he must do something to make up for it.

"Ransom": Gerald and Arnold get on the case when Timberly's doll goes missing.
"Ms. Perfect": Lila, the new girl, is disliked at school by Helga and the other girls for seeming to be absolutely perfect and a big hit with all the boys. The girls soon play a prank on Lila, causing paint to spill all over her in front of the school. They soon accept her after they see how upset she is and learn that her dad has been unemployed for some time, leading to the two having little to no food in the house.

"Freeze Frame": Arnold and Gerald go around the city following "Porkpie", a mysterious man caught on film. They suspect, because of the clues, that Porkpie are planning to kill "Marty", who turns out to be Mr. Green.
"Phoebe Cheats": In this variation of "The Tell-Tale Heart", Phoebe plagiarizes from a poetry book and uses one of the poems as her entry in a poetry contest. She wins, with her prize being a trophy resembling poet Emily Dickinson. Then, the trophy haunts Phoebe into confessing.

"Steely Phil": Arnold's Grandpa enters a Chinese Checkers tournament to reclaim his pride lost forty years ago.

Note: Robby Fisher's name is a parody of Bobby Fischer.

"Helga's Boyfriend": Helga uses Stinky as her boyfriend to try to make Arnold jealous.
"Crush on Teacher": Arnold becomes infatuated with Miss Felter, a substitute teacher, thinking she returns the feelings and that they are having dinner at her house. He later realizes that the one she invited was her fiancé, whose name is also Arnold.

"Hall Monitor": Phoebe becomes hall monitor and asks Helga for tips. She becomes overwhelmed by the "power" and soon everyone wants the old Phoebe back – even Helga, once she realizes Phoebe's also giving her detentions.
"Harold's Bar Mitzvah": Harold runs away from his Bar Mitzvah, thinking he will retain his childhood this way.

"Runaway Float": After creating an idea for a parade float, Arnold is confident of it showing up in a parade.
"Partners": A lounge singer moves into the Sunset Arms after renouncing his songwriter, who also moves there.

Guest star: Harvey Korman as Don Reynolds

"Dangerous Lumber": Arnold has a lethal baseball bat swing, causing him to unintentionally knock out other players, so he decides never to play the sport again, mere days before a baseball game against the fifth graders.
"Mr. Hyunh Goes Country": Mr. Hyunh has a talent for country singing, so Arnold and Gerald, after recording a CD with him at the local studio, become his managers and make him a big star, much to his dislike. Their biggest gig is on-stage the Grand Ole Opry, Mr. Hyunh's favorite show. Mr. Hyunh must decide to become world famous and tour or not.

"Curly Snaps": Curly locks himself in the principal's office after being skipped as Ball Monitor, the person who collects kick balls after recess.
"Preteen Scream": Phoebe wins a chance to meet her favorite singer, only to find out that he does not write or sing his own songs, he’s just a self-centered pretty boy.

"Phoebe Takes the Fall": Helga demands that Phoebe lose a quiz competition to impress her competitive father.
"The Pig War": Arnold, Grandpa, and friends reenact the Pig War.

"Crabby Author": Arnold does his school report on an author he likes, only to find out that she's a grouchy, old witch.
"Rich Kid": Lorenzo, a neurotic rich kid, comes to P.S. 118. All the kids try to help him become an average kid.

Guest star: Rose Marie as Agatha Caulfield

"Full Moon": Harold, Stinky and Sid accidentally frame Arnold for mooning Principal Wartz, despite him being an innocent bystander.
"Student Teacher": Helga's sister Olga comes home for spring break and becomes a classroom aide in Helga's class, much to Helga's dismay.

"Eugene's Birthday": After losing Eugene's birthday party invitations, Arnold feels obliged to throw him another party, but it does not work out.
"Stinky's Pumpkin": Stinky grows a huge pumpkin to enter in a city competition to prove he's good at something, despite his family telling him nothing has grown on their land for years.

"It Girl": Helga becomes a model, but she quits after she gets irritated at everyone dressing like her.
"Deconstructing Arnold": Arnold's classmates are tired of constantly telling them the right thing to do, so he stops giving them advice. Nevertheless, when his classmates get into sticky situations, they are in desperate need of it.

"Grandpa's Sister": Phil's twin sister, Mitzi comes for a visit, bringing along an unsettled conflict between them.
"Synchronized Swimming": Arnold and the guys are part of a synchronized swimming team led by Coach Wittenburg.

"Helga Sleepwalks": After eating pork rinds, Helga sleepwalks, uttering her secret about Arnold as she does so.
"Fighting Families": Arnold, Grandpa, Grandma, Ernie and Mr. Hyunh compete on a game show against a "perfect" family from PS 119.

Guest star: Ryan Seacrest as Fighting Families Host.

A child psychiatrist, Dr. Bliss, shadows students at PS 118, quickly following Helga and noting her behavior, especially towards Arnold. After punching Brainy in the face, Helga is sent to Dr. Bliss's office for an appointment. Helga confides in Dr. Bliss about her social life, family life and her secret crush on Arnold.

Dino Spumoni is found missing and then declared dead after what appears to be a suicide attempt. but Arnold finds out that this is not the case, and he secretly lives in the boarding house, believing that his work will skyrocket in value after his "death".

Guest star: Harvey Korman as Don Reynolds

"Monkeyman!": When Arnold gives the superhero Monkeyman a taste of normal life, he is far too busy to bother helping the weak and downtrodden. He realizes what he has become after Sid is mugged in front of a big party Monkeyman is attending.
"Buses, Bikes, and Subways": Helga and Harold must return to town on their own after the bus leaves them behind after a school trip to a chocolate factory, and Helga has tickets for a wrestling match and she cannot be late.

Guest star: Andy Dick as Monkey Man

"New Bully on the Block": The kids must face two older bullies when a new kid, Ludwig, returns from some time in juvenile hall and challenges Wolfgang for the vacant lot.
"Phoebe Breaks a Leg": When Phoebe breaks a leg after being hit by a bus, Helga believes it is her fault, so she starts being nice to Phoebe. When Phoebe's leg heals, she decides to stay disabled for a little longer.

"Suspended": Harold gets suspended and will do anything to get back into school once he grows bored with being at home all day.
"Ernie in Love": Ernie becomes attracted to a tall, kind, beautiful, plus-sized model named Lola. Arnold convinces him to build up courage to ask her out on a date to the pier, which she accepts. After the date, she tells him she had fun, but is unsure about another date because of his height.

It is time for the school's annual "Parents' Day", a weekend of competition with teams of a kid and their parents. Arnold feels odd about bringing his grandparents, as they are his parents, who he has not seen since he was a baby. After Big Bob calls Arnold an "orphan boy", Arnold asks Grandpa Phil what really happened with his parents, and he finds out that they disappeared after they left the country on a plane, delivering medicine, although they might still be alive. Arnold continues on with Parents' Day, with Phil and Gertie. He realizes even though they are not his parents, they raised him and made him who he is, which is what parents do.

When Arnold, the boarders and the Patakis go to the beach, a girl uses Arnold to win a sandcastle competition. Ernie gets buried in the sand. Miriam and Suzie start taking dance lessons from a handsome dance instructor named Carlos. Grandpa Phil thinks he is stuck on an island. Oskar starts using a metal detector to find "treasure". Big Bob gets a bad sunburn. Helga tries to warn Arnold that he is just being used.

Guest star: Beverly Mitchell as Summer

"Beaned": When Helga gets hit with a baseball during a game, she develops a case of amnesia, so Arnold stays with her all day because he feels responsible. The next day, Helga regains her memories, though, when she realizes what Arnold did for her, she decides to continue to play the part of an amnesiac in hopes of spending more time with him.
"Old Iron Man": Grandpa Phil and his old friend, Jimmy Kafka, have been feuding for quite some time, as their friendship fell apart years ago. However, they still attempt to compete with one another as they each believe they are the better individual; though when both men decide to enter the extremely dangerous Old Iron Man triathlon, Arnold attempts to put an end to their feud, as he does not believe they should risk their lives over something so trivial.

Guest Star: Richard Mulligan as Jimmy Kafka

"Harold vs. Patty": After Harold loses to Patty at arm-wrestling, Sid and Stinky won't let him live down the fact he lost to a girl; so in order to regain his stride, Harold seeks Patty out twice: first for a rematch, then to help him retrain.
"Rich Guy": When Arnold stops a hockey puck from hitting a rich man, the man treats Arnold as "the son he's always wanted". Arnold is fine with this until he discovers the man actually does have a son of his own and tries to help the two have a better relationship.

"Gerald's Game": Gerald is involved with his new favorite game, which Arnold dislikes.
"Fishing Trip": Arnold, Gerald, Harold, Sid and Eugene go on a fishing trip with their fathers and Phil.

Guest star: Davy Jones as himself

Arnold finds his father's old journal, which tells the story of how his parents met, how they got Abner, his birth, why they went on their "last" trip...and one last surprise...

Note: This episode was copyrighted in 2001. These were the final episodes produced; originally designed as a cliffhanger as a lead-in to "The Jungle Movie", a theatrical feature that was cancelled and then revived years later as a two-part television film.^[50]

"Timberly Loves Arnold": Gerald's little sister, Timberly develops an crush on Arnold after he sticks up for her and lets her hang out with them. Arnold is embarrassed at first, but when he finds out that Lila considers this admirable of him, Arnold is content to keep his mouth shut and let the charade continue.
"Eugene, Eugene!": Eugene gets the lead role in the 4th grade production of "Eugene, Eugene", but the embitttered director, Mr. Leichliter, removes all signs of hope from the script, having changed the ending himself to reflect real life (it is apparent he was influenced by his own past relationship with a woman). Meanwhile, Lila gets the role of the leading lady in the play and with Arnold playing the villain pursuing her, Helga attempts to sabotage her during the play.

"Ghost Bride": Gerald tells the story of the Ghost Bride, Cynthia Snell and how she brutally murdered her fiancé after he left her waiting at the altar and married her sister, who she also murdered. When the police came to the scene, she was still there, sitting in a rocking chair, in her wedding gown, tossing rice on the bodies as she hummed the Wedding March and before they could arrest her she jumps out of the second-story window and killed herself instantly. She also happens to be buried in the cemetery near the gang's neighborhood and supposedly comes back from the dead every anniversary of the murder. Arnold, Gerald, Eugene, Harold, Sid and Stinky are scared twice by Helga and Curly, each pretending to be the Ghost Bride (Helga because she wanted to get back at the boys for not letting her come with them because she was a girl and Curly because he was jealous he didn’t get to tell the story). As punishment, the kids tie up Curly in the crypt, where at the end, he hears the real Cynthia Snell, although it's possible that he was only hallucinating.
"Gerald vs. Jamie O": Gerald gets jealous because he thinks Jamie O. is trying to steal the girl he likes, when, actually, the girl likes Jamie O, and using Gerald to get close to him.