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- "I knew I should've stayed home today!"
- —Arnold whenever he feels uncomfortable at school or during a field trip.
Arnold in particular, usually has a dislike on field trips. Most of the time, he is usually an unwilling participant. Despite his usually timid moments and some nervous breakdowns, he has shown to have a brave personality when he's needed to, and he's very loyal when it comes to his classmates, even taking up a leadership role a number of times. He has a huge interest in rocks and minerals, and is the youngest member of GRANITE (the Great Rock Admirers' National Institute of Tectonics Experts), an organization for amateur geologists. He also mentions an interest in colors. He has shown interest in conserving the environment, as he wanted to save the rotting log in "Meets the Rot Squad" and have the class collect stuff for recycling in part 1 of the Holiday Special.
Despite his paranoia for field trips, he does love having the Frizzles as teachers, and deep down, enjoys the adventures, but is too nervous to show it and he doesn't usually like surprises. He even stood in her defense when the class went on trial during the original series episode "In a Pickle" and when his cousin, Janet, tried to show off and say that her teacher is better than his, Arnold interrupted her before she could finish and said, "Nobody is better than Ms. [Professor] Frizzle" during "Gets Lost in Space". When it comes to riding the Bus, Arnold just likes to stay safe because of all the dangerous happenings, but he genuinely and deeply does care for his friends and the Frizzles, and enjoys a wonderfully wild ride on the Magic School Bus (just not too wild).
Appearances and clothes
In the original series, Arnold's appearance is similar to his book counterparta. Arnold is a bespectacled boy who wore a yellow-and-white striped polo. He wore blue jeans and blue sneakers for leg- and footwear. but in this canon, he has curly red hair instead of curly blond hair. The light-blue circular-framed eyeglasses, the yellow and white striped long-sleeved polo shirt, blue jeans and navy and white sneakers are the same as in the books. In the Rides Again series, his hair was cut into a bowl. He wears rectangular glasses instead of circular-framed glasses, and he wears a green sweater over his trademark striped shirt. His facial features are shown much more clearly, and he is revealed to have freckles and green eyes.
In the original series, his signature colors are yellow and blue, but in Rides Again, the yellow is replaced with green. His newer design is most likely based on Phil, another character from the book series.
Arnold introduces his cousin, Janet, to his class in "Gets Lost in Space", and he tries to keep the peace when Janet's arrogance sours the rest of the class. It's when Janet talks down on Ms. Frizzle that he shows his loyalty to his teacher and suggests a field trip to the "bigger" planetarium, showing Janet that "nobody is better than Ms. Frizzle." Arnold unknowingly eats the class in "For Lunch". He's happy to have stayed behind while the others go on a field trip, but after finding out where they went, he swears never to miss a field trip...at least, not until after the "next one" (Ms. Frizzle's dinosaur dress foreshadowing the next season). He and Keesha find themselves in a difficult situation when they forget their partner report in "Gets Eaten". He loses Wanda's bullfrog, Bella, in "Hops Home" and tries to keep her out of harm when they look for Bella, as Wanda's too distracted to realize she's about to walk off of a tree or get swept down a river. In "Meets the Rot Squad", he tries to convince everyone to leave the rotted-out log on the abandoned lot the way it is. Everyone is shocked when he suggests that they take a field trip to the desert in "All Dried Up" after Phoebe declares they need to help the animals there. He feels confident about the trip, thanks to his Field Trip Survival Guide.
While on a field trip to a dinosaur dig in "The Busasaurus", Dr. Carmina Skeledon lets Arnold see the fossilized egg Ms. Frizzle found. He still has it when they go back in time, and when he lets Phoebe look at it, she loses it to an Ornithomimus. He ends up squaring off with a Tyrannosaurus Rex after Ms. Frizzle makes him giant-sized, saving the class. In "Butterfly and the Bog Beast", he's the only one not to side with Janet against Phoebe when the former suggests "Bog Beast" for the school mascot. His main reason is because he doesn't know what a bog beast is. He's caught by his crush, Tiffany, when he and Wanda get water from the girls' bathroom in "Wet All Over". Despite the embarrassment, it's implied at the end that Tiffany likes him, too. He serves as Ms. Frizzle's defense attorney in "In a Pickle". While in the bus' gas tank, Arnold says that he hates the smell of gasoline and was out on the engine telling the class what was going on while they were in the cylinder in "Revving Up".
After losing the heat from his hot cocoa, Ms. Frizzle takes the class to the Arctic ("In the Arctic"). When Ralphie, Phoebe, Liz, and the bus get stranded on an ice flow, Arnold makes it his responsibility to save them while also trying to keep everyone else warm. He and Dorothy Ann compete in the 10th Annual International Show and Tell Competition in "Shows and Tells", but instead of bringing a rare collection of rocks, he brings some artifacts he found in his attic that belonged to his great-aunt, the famous archaeologist Arizona Joan (a parody of the film character Indiana Jones). In "Rocks and Rolls", he fears that the statue he was supposed to carve (not by hand) is ruined, but instead, the rock slide the class caused on the side of a mountain carves a monument of the town founder. For the class' last day before winter break in "Holiday Special", Arnold made the suggestion they collect recycled goods to take to the recycling center. He accidentally puts Wanda's beloved toy soldier in the pile, causing her to blame his "crummy idea" and wish that recycling had never been invented.
Ralphie teases Arnold in "Meets Molly Cule" after the famous rock star, Molly Cule, calls him "Sugar.", this caused Arnold to blush. However, this is what helps him figure out that her hood ornament was made of sugar. In "Cracks a Yolk", Arnold helps hatch the chick the class planned to replace Mr. Ruhle's lost rooster, Giblets, and the success prompts Dorothy Ann to kiss him. When Giblets returns, Mr. Rhule gives the chick to Dorothy Ann and Arnold, the latter suggesting they name it "Arnold Jr." In "Goes Cellular", he's completely orange on the night he's to receive GRANITE's Rocky Award. The class tries to compare his skin to Phoebe's, only to learn his favorite snack food made him turn orange. He's happy when Ms. Frizzle's electrician wants to buy all the light bulbs the class was trying to sell for Valentine's Day ("Gets Charged"). He becomes a fox along with Phoebe and Tim in "In the City", and he's partners with Phoebe in "Takes a Dive".
In "Frizzle of the Future", Arnold was unhappy to see that his favorite teacher, Valerie Frizzle, has become a research professor with a Ph.D and a new teacher, her sister, has replaced her. In "Pigs in the Wind", he plays the part of pig 3 in The Three Little Pigs 2. In "Hides and Seeks", he joins Dorothy Ann and the rest of the kids in the rainforest to help Jyoti, Tim, and Ralphie win a game of Walkerville Elementary School's annual Ultimate Hide and Seek.
In "Making Magic", Arnold is so excited to go on a field trip to the beach, but instead they end up going to the actual sun with Mr. Ruhle to charge the Bus's battery. In "Kids in Space", Arnold takes on the role of safety officer during a field trip to the International Space Station. In "The Frizz Connection", it's his birthday and he decides to attend the International Balloon Festival in Albuquerque, NM as his "birthday field trip" on the Magic School Bus. Along the way, a strike of magic lightning affects Ms. Frizzle, causing her to split into three emotions: Goofy, Reliable, and Adventurous. The class (including Liz) is sent to different parts of the world, and he, DA, and Liz end up in Nova Scotia, Canada, with the reliable-teacher side of Ms. Frizzle. In ''In the Zone", he and the class join another cousin of the Frizzles, Maven, on her world tour for New Year's Eve.
- His parents first appear in "Going Batty," his father voiced by Elliott Gould. They make another appearance in "Rocks and Rolls" and "Goes Cellular". Mr. Perlstein also appears in "Holiday Special". Arnold seems to take after him, since in "Going Batty", he said "Maybe we should've stayed home tonight."
- His only cousin is his paternal one, Janet Perlstein, whose personality mirrors his.
- His great-aunt is the famous archaeologist Arizona Joan ("Shows and Tells").
- He mentions his grandmother in "Holiday Special", and later in Janet's Mystery Gene. Assuming because his mother is already with her, she's his maternal grandmother.
- His grandpa was mentioned in Janet's Mystery Gene during the Freckle Gene Machine, but he never appeared in person.
- His paternal grandmother was also mentioned in Janet's Mystery Gene.
- His son, Arnold Perlstein Jr., is shown in “Frizzle of the Future” when the class travels thirty years into the future. He appears with the other students’ children and their teacher.
Producer Says segments
As the caller
- Makes a Stink/Producer Says
- Frizzle of the Future/Producer Says
- He is the third student to have a birthday within an episode. It was celebrated in "The Frizz Connection", and happens on the first full week of October (his birthday is celebrated during the Albuquerque International Balloon Fiesta).
- In the television canon, he has been the most-explored human body, behind Ralphie. ("For Lunch", "Goes Cellular", "I Spy with My Animal Eyes")y
- In Tim's comic-book universe, The Adventures of Weatherman, he is named Captain Rock Man.  
- Arnold's favorite color is orange .
- In the Arabic dub of TMSB, his name is Fareed.
- He is Jewish. 
- His surname, Perlstein, is Ashkenazi (German/Yiddish).
- Bruce Degen mentioned that a friend of his son's was the original model for Arnold.
- He has two allergens: pollen and pepper.  
- Arnold's favorite drink is hot cocoa, because he enjoys the winter. 
- While crushes are only hinted at, Arnold's had affection shown to him for and from four girls: Wanda ("For Lunch" (him fantasized himself breaking a record and her hugging him), "Holiday Special" (she was his secret Santa), "Hops Home" (they teamed up), "Meets the Rot Squad" (she imagined herself sitting under a tree with him) and "Gets Charged" (they were cupids at the end of the producer segment)), Phoebe (The opening credits (he held onto her shoulders and she smiled while they were rafting a river of lava) "The Busasaurus" (she swooned over his bravery) and "Goes Cellular" (she helped him when he was orange)), Tiffany ("Wet All Over" (he helped her up and held her hands at the end and blushed)), and even Dorothy Ann ("Gets Ready, Set, Dough" (he hugged her after she and Carlos got them out of the cake), "Shows and Tells" (They were supposed to do a show and tell together, but he managed to do it without her help, and they held up the trophy upon winning the Show and Tell competition) and "Cracks a Yolk" (she kissed him out of gratitude and he proceeded to blush).
- While often cautious and nervous about field trips, he has never had a phobia revealed, unlike Carlos and Phoebe.
- Arnold flew on an eagle. 
- Arnold's been shown to be a big eater with Cheezie Weezies, Sea Wheedies, and Mallowblasters being among his favorite snacks. 
- It's possible he had some fight lessons, considering the boxing stance and martial arts he uses in "The Busasaurus", this was also implied in the book "Ms. Frizzle's Adventures: Imperial China".
- Arnold despises the smell of gasoline  and the taste of pickle juice 
- His and Janet's book counterparts have blonde, curly hair instead of red, straight hair.
- Also, it is implied that the Perlsteins use hair curlers.
- He is mentioned a lot of times in the producer segments.
- In the Spanish dub, his name is Arnoldo. In the German dub, his name is Andy.
- He and Tim are the only main kids in the original series to have had their voice actors changed in the 2nd season. He had been voiced by Amos Crawley in the 1st season. He was voiced by Danny Tamberelli in the 2nd-4th seasons due to Amos going through puberty after production for the 1st season ended and sometime before the 2nd season was in voice production, his voice was already too deep for him to continue voicing him. The difference between the two voices is that Amos is Canadian, and Danny is American.
- His second voice actor, Danny Tamberelli, also played the character Little Pete in The Adventures of Pete & Pete. He would later move on to working as a cast member of the sketch comedy show All That, and even later voiced/mocapped Jimmy De Santa in the 2013 Open-world Adventure game Grand Theft Auto V.
- In the last few episodes of the original series, Arnold's voice was noticeably getting deeper and nearly teenager-like despite being ten like everyone else in his class. The reason for this is because Danny was starting to go through puberty at the time.
- He broke the fourth wall in "For Lunch", saying he would never miss another field trip, starting right after the next one, facing the viewers as he said it.
- He was the first character to let the class enter his mouth and explore his body, which happened in the book Inside the Human Body.
- Whenever he is seen in the dark such as "In The Haunted House" and "Gets a Bright Idea" (along with Janet), his shirt would sometimes turn green and his hair sometimes turn brown.
- Arnold has an aunt who is a nurse. 
- Arnold is the first major character to change voice actors due to his voice actor going throughout puberty. His original voice actor, Amos Crawley, was swapped in for Danny Tamberelli, and later Miles KV and Roman Lutterotti.
- Arnold is the only student who wears glasses.
- Arnold likes rock operas. 
- Arnold is bad at sports. 
- Arnold is the fourth major character revealed to have grandparents, mentioned in Janet's Mystery Gene and Holiday Special. The first being Ralphie in Inside Ralphie, the second being Keesha in Going Batty, and the third being Tim in In a Beehive.
- Arnold, Carlos, Keesha, and Phoebe all have six letters in their English names:
- Arnold has six letters in his French name (Arnaud), but seven in his Latin American and Russian names (Arnoldo and Арнольд)
- In the game Explores in the Age of Dinosaurs, he is one of two kids to appear in all three time periods with Keesha being the other.
- He is one of only four students to also have book counterparts appearing in all 13 original books, the others being Dorothy Ann, Wanda, and Tim.
- Arnold is one of the 7 students known to make a pun along with Tim, Ralphie, Carlos, Phoebe, Keesha, and Wanda.
- Arnold appears to be ambidextrous, or else his dexterity differs between the book and animated canons. 
- Arnold’s catchphrase has been referenced, unknowingly or not, in popular culture.
- In the YouTube web-series, SMG4 (2011–present), Meggy Spletzer uses his catchphrase in the episode, "The Pursuit of Happiness". In this iteration of the catchphrase, it is worded as "I knew I should've just stayed home today!"
- In the English version of the 2020 RPG video game, Genshin Impact, Lisa uses his catchphrase whenever she is is knocked out. However, "today" is omitted.
- Revealed in Ms. Frizzle's Adventures: Medieval Castle
- The Battle for Rock Mountain
- In the Zone
- Makes a Rainbow, Goes Cellular
- Holiday Special
- Goes to Seed
- Meet the Class
- In the Arctic
- Taking Flight
- For Lunch
- Revving Up
- In a Pickle
- Gets Ants in Its Pants
- Waste Not, Want Not
- Ready, Set, Fail!
- The Magic School Bus at the Waterworks, In the Zone
|Walkerville Elementary School|
|Mr. Ruhle (principal) • Mr. Wilde (assistant principal) • Mr. Quiggin (librarian) • Mr. McClean (janitor) • Ms. Frizzle (fifth grade teacher) • Professor Frizzle (retired)|
|Ms. Frizzle's class|
|Arnold Perlstein • Carlos Ramón • Dorothy Ann Hudson • Jyoti Kaur • Keesha Franklin • Ralphie Tennelli • Tim Wright • Wanda Li • Book Extras|
|Janet Perlstein • Tiffany • Mikey Ramón • Harry Arm • Seeker|
|At other schools|
|Arnold · Janet|