She is the former class president of Kick's class and used to be anti-heroine in the show. She originally dislikes Kick Buttowski for his daredevil personality, except in some episodes like in "Dancing With The Enemy", and "Hand in Hand".
Kendall is usually a tough, bossy and tomboyish young girl, but is a very good and intelligent student. She has very rarely failed a class (one or twice in one 6 months) and is a straight A student who earns mostly the highest marks (A-, A, A+, and even A++) although in "Frame Story" she only manages to earn a D- (51-60) due to Kick's failure at cooking.
As class president, she holds a great deal of responsibility within the school (that is until "Poll Position" when she loses the class presidential election to Gunther). She is always annoyed by Kick, to which she refers to him by his first name, Clarence. Because she likes elegance, she doesn't break any rules (except in "Detained", in which Ms. Chicarelli puts her in detention). To Kendall, elegance and rule-breaking are polar opposites of each other. When she gets really angry, she becomes a very scary girl (nearly a monster) who screams louder than anyone. She is simply bossy and a little mean; she is also not too friendly with people whom she considers idiots (like Gunther, as seen in "Abandon Friendship!" and "Pinch Sitter").
Ronaldo at the time was her actual boyfriend starting from the episode Frame Story, but it is hinted that she has a secret crush on Kick, which can be seen in many episodes, as in the entire series way before she met Ronaldo. When they're together, Kendall will always begin to warm up to Ronaldo. But once he does something stupid, she usually gets very angry at him and becomes a very scary person.
She is also shown to be very knowledgeable about technology as she is able to activate Ronaldo's force field without his help in "Stand and Delivery".
Kendall is one of the tallest girls in Mellowbrook Elementary School, along with Jackie Wackerman. She has chest-length blonde hair and, like the majority of the characters, has black eyes. Her usual attire consists of a pink and green argyle sweater which she wears over a white shirt with thin blue stripes and a dark grey skirt with white knee-high socks and black shoes. On her head, she wears a pink headband. In "Pool Daze", she is seen wearing a green swimsuit with pink and white stripes. In "Gym Dandy" she is seen in her gym uniform and black slippers with white stripes. In "Tattler's Tale" and "Roll Reversal" she is seen wearing a jumpsuit which is very similar to Kick's own. She is also seen wearing sports clothing in the Roller Derby in "Roll Reversal".
"Stupid thing? So now the giant wooden statue of me is just a STUPID THING??!!"
Kendall is seen as a "convinced-by-herself" girl because of her school life, her A-,A,A+,S grades and her occupation as class president. She usually dislikes lots of people (like Kick and his friends), which makes her kinda mean and is the reason why she doesn't have many friends. But she, on the inside, has a heart of gold. She can be really sensible, friendly and emotive, but in episodes like "Kick or Treat", she is shown to be arrogant and selfish. However in "Pinch Sitter", Kendall can be quick on her feet and outsmart Kick and Brad when she babysit them. In "Roll Reversal", when she accidentally step on Kick's skateboard and did the motocross without the moto, she (even though it was a for a short time) had some friends and feels appreciated for an accomplishment, and since it was originally Kick's stunt, Kendall is in a playful mood while teasingly rubbing her success in Kick's face.
Nevertheless, Kendall can get really angry at times, mainly with Kick or sometimes with Ronaldo. In "Stand and Delivery", Ronaldo insults the statue that Kick (not Ronaldo) made or in "Faceplant" Ronaldo makes something stupid like replacing chewy nuggets with atoms in chocolates for Kendall, she becomes furious enough that she becomes a very scary girl. Most of the time she can't handle rule-breaking and rebellion (although in "Detained", she reluctantly joins forces with Kick and the other detained kids in order to escape detention).
As shown in "Dancing With The Enemy", she is a very talented and fearless dancer, being seen as very agile and strong on stage. And she was able to earn lots of fans because of her impressive and elegant dance abilities.
In "Hand in Hand", her awesome side is discovered. With her quick-thinking and clever ideas, she is able to help successfully keep a lid on her "stuck hands" situation with Kick. Throughout the episode, she is also shown to be a fearless girl, becoming more accustomed to Kick's stunts. And Kick likes her awesome side in prior of the same episode. But when she gets really upset, she becomes very scary. In "Roll Reversal" Kendall unintentionally outdoes Kick at a Motocross stunt that he is about to perform himself.
Family and Early Life
Not too much is known about Kendall's early life or of her family. Her father, Mr. Perkins, is an actuary as shown in "Father From the Truth". It is hinted that Mr. Perkins is associated with Mellowbrook Elementary since in "Snowpocalypse!", she wants him to open the school even while it is snowing in Mellowbrook (and he did it). Her mother, Amy Perkins will never appear on the show  because she lives in a different town . It was also confirmed by Sandro Corsaro that Kendall has an older sister and although she is mentioned by Kendall in "Pinch Sitter", she won't appear in the show herself due to it ending although a background character with her planned design does have a cameo role in some episodes.
At school, Kendall can be considered a "princess" - she is the class president of Kick's class (until "Poll Position"), often gets almost perfect/perfect marks and is also the smartest student in the entire school (even smarter than Ronaldo). But despite all this, Kendall can get rather... lonely. She doesn't have many friends, due to her mean and bossy personality. In "Dancing With The Enemy", however, her talent for dancing managed to attract many fans.
It is possible that Kendall may marry Kick when they become adults, since both are hinted to have a crush on each other. Or, she may marry Ronaldo, since she actually dates him. However, since KB: SD has not been renewed for a third season, it's highly likely that any romantic relationships in the show will be left unresolved. Despite this, when asked what will become of Kick and Kendall, Sandro Corsaro replied on his Twitter page that we "can't have one with out the other" (meaning that we can't have Kick without Kendall and vice versa). Also when asked if their love/hate relationship would remain unresolved Corsaro replied, again on his Twitter page, that Kick and Kendall "will always have a connection" (but to what extent is not expanded upon). When asked what the future would hold for the two characters on his Facebook page, Corsaro replied "Somehow, I think they both end up pretty happy in life :)". When asked if the two would be together (again on his Facebook page), Corsaro replied "Maybe...you never really know what the next day can bring;)".
Kick and Kendall have been shown to argue many times, and both proclaim to dislike each other intently.
In "Snowpocalypse!", she is able to force Kick and the rest of her classmates to go to school, much to his and their displeasure (their school is the only one on earth without a snow day, thanks to Kendall). However, it has been shown on a few occasions that they seem to have what amounts to a romantic liking for each other.
In "Dancing With The Enemy", they are forcibly paired together to dance, but eventually enjoy it and compliment each other in the end. However, when an unknown female person in the crowd shouts "Kiss her!", they almost immediately revert back to their old ways.
In "Hand in Hand", Kendall and Kick get both of their hands stuck together. While working on getting their hands unstuck, they blush and kiss each other (but only to hide it from Ronaldo).
Later in "Detained", Kendall gets sent to detention by Ms. Chicarelli and helps Kick get her fired. Later, when Ronaldo asks what got her in detention, she says that it was just a misunderstanding with her favorite pink pen, to which the camera then zooms in on "I ♥ K.B." written on a locker; officializing her crush on Kick.
In "Power Play", during the school's production of Romeo and Juliet, she takes out a peg that had been holding a sandbag on the roof, letting it fall on Ronaldo's head so that Kick takes his place as Romeo. She also says, "Time for that kiss!" and looked disappointed when Kick succeeds in knocking himself out just before the kiss.
In "Poll Position" Kendall smiles (almost breaking into tears) when Kick offers to help her.
In "Roll Reversal", Kendall accidentally outdoes Kick in a motocross stunt without the moto, and gets praised, and she went along to teasing Kick and making him jealous with her exaggerated action of the moto. Kick dares Kendall to pick a challenge, she picks the roller-derby (which is girls only, which means Kick has to cross-dress). Later in the roller-derby, before Kick could finally beat her, Kendall stands in the way by kissing him.
It is revealed in "Frame Story" that Kendall and Ronaldo are in a secret relationship. Kick discovers this accidentally while claiming that the two are the ones who framed him, noticing that they are both holding hands. Kick manages to swipe a drawing of the two out of Kendall's hand, causing him to get sick and leave the room. Afterwards, Ronaldo is about to read a poem to Kendall, but after he says it is written in only ones and zeros, Kendall calls him the "worst secret boyfriend ever."
It is possible that their relationship might end soon. In "Power Play", Kendall and Ronaldo are leads in a play of the classic Romeo and Juliet. Even though Ronaldo is chosen to play Romeo, Kendall actually wants Kick to play the part. She eventually succeeds in making Kick play the part by pulling out a peg which is holding up a sandbag and causing it to fall on Ronaldo's head.
Their relationship can also be seen in "Stand and Delivery", "Faceplant!", "Hand in Hand", "Detained", "Kick or Treat" and "Poll Position".
It is possible that their relationship has ended off-screen because in "Roll Reversal" he is impressed when Kick inadvertently becomes the smartest student in the class, Kendall is angry with Kick but Ronaldo isn't.
While Jackie sees Kendall as an enemy and rival for Kick's love, Kendall just sees Jackie as an annoyance, and likely doesn't see her as a rival in that way. But in "Roll Reversal" Jackie is her biggest fan.