Lee Ping(Jonathan Tan) - Lee is the main protagonist of the series and is the titular Detentionaire. He is Korean-born/Canadian and a straight-A student, except for Gym in which he got a C. On his first day of school he was framed for a mind blowing prank and thus received detention for one full year and grounding for the same length of time by his mother. Every day since he's had to sneak out of detention so that he could collect evidence to clear his name. It turns out that he has had a crush on Tina Kwee since the Fifth Grade. His first name is common in the West and his surname is an actual Korean family name under theMcCune-Reischauerromanization; his full name is mistaken for the word "leaping" in the first few episodes by Brandy Silver.

看本吧头像，我就不发图了～

Camillio 'Cam' Martinez(Fabrizio "Fab" Filippo) - Camillio or called 'Cam' is Lee's childhood best friend. Though loyal to Lee and helps with his endeavors when he can, he'd just as soon ride Lee's new found wave of popularity as long as it will last (as being blamed for the prank had made Lee the most popular student in school). Camillio shows a rather strong interest in finding a girlfriend, which drives his motivation to try and keep Lee from openly denying his status as the prank perpetrator, as Lee's fame helps Camillio score attention with girls. It is hinted he has a crush on Lee's girlfriend Brandy, they went to a concert together with Holger and his date. In "The Curse of Earl Nigma", Cam buys a finished book report from a genius, and ends up getting blackmailed by an unknown person.

Holger Holgaart(Ryan Belleville) - Holger is Lee's overly loyal friend and A. Nigma High's Scandinavian exchange student. Though he appears and acts incompetent in all things, on occasion having to be bailed out of trouble by his friends, the value of his few skills have proven to exceed his incompetence. He's proven to be stealthy, easily running circles around Barrage, and his knowledge of Spa and Cooking got him the position of Water-boy, which he was able to use to find out whose hand was in a picture of someone messing with Lee's bag. He has a crush on the uni-browed mathlete Greta, who likes him back.

Cam and Holger！～

Biffy T. Goldstein(Zachary Bennett) - Though he's publicly a bully, especially towards Lee Ping, Biffy is a gentle giant with a soft spot for his pet cat Rumble kitty. Biffy helps Lee for reasons only known to him using his technological savvy, ingenuity, and intimate knowledge about the school and what's happening inside to guide Lee and track people of interest throughout the school. Despite helping him on numerous occasions, Lee is certain that Biffy will kill him one of these days. His favourite band is the Dudes of Darkness and loves a good rock tune. Later on, it is hinted that he and Kimmie knew each other, and (in the present) might have a "thing" for each other. In later episodes he has often showed compassion to the quirky Holger, who is riduled with misfortune.

Tina Kwee(Krystal Meadows) - Tina is another childhood friend of Lee, and is Lee's secret crush. She's one of the school's news reporters, and does show a strong passion for it, however her rivalry with her senior school reporter Chaz Moneranian tends to make it harder for her to get what she wants. She's also up to help Lee and his friends as she helped find the owner of the e-mail address which sent the e-mails to different people whom participated in the prank. She is also out to unravel the mystery of A. Nigma High's growing list of missing teachers and staff (being replaced by Barrage,) shown in a series of shorts available exclusively on Teletoon's website.

原谅我……网上的图真的太少了，都是自己截的0.0

Brandy Silver(Melanie Leishman) - Brandy is bossy and popular. She told Lee that she was his girlfriend after the prank and Lee was her first kiss (episode 2). She is in the clique Glamazons which think Brandy is not always what a 'Glamazon Girl' should be. She has blackmailed Lee a few times, threatening if he doesn't do something she wants she will tell Barrage that Lee has been sneaking out of detention. She doesn't like Tina since she knows that Lee likes her. She cares about her appearance and popularity and is commonly seen in the hallways ordering people around or putting them down, but she does seem to have a kind heart. She later gives up on Lee and starts a relationship with Cam.

Chaz Monarainian(David Berni) - Tina's competition and co-anchor on the school's news program. He is always pushing Tina out of the camera and read out her share of news. Chaz hosts his own show called 'Chaz's Corner'. He is self-absorbed, obsesses about his appearance, and likes to hog the camera. He had footage of the prank which Lee obtains and discovers who switched his bag. He is also scared of getting sick and having messy hair. He has flirted with 'Glamazon' Queen Kimmie. His father as seen in episode 5 is also a news presenter. He gets suspended from the news desk in episode 14 and is jealous of Tina.

Principal General Dr. Wendell Barrage(Seán Cullen) - Barrage is the new principal of A. Nigma High. A former Black Ops general with a classified pass, war amputee and above all is a fearsome looking cyborg. He has a no nonsense attitude and ruthless in all things. He firmly believes that Lee Ping was responsible for the prank and has made it a hobby to drag him to detention at every available moment. Barrage doesn't seem to be shy about his experience in the military, as he's taken much of his enjoyment, standard, and training methods with him to the school. He held the football tryouts using artillery cannons to throw the balls at the new 'recruits'. He's easily distracted by things military related, as he confiscated a phone which at the time had a game playing on it involving tanks, which distracted Barrage for most of Lee's detention period.

The Tazelwurm- The Tazelwurm is a red lizard-like creature of unknown species that serves as the mascot of the school. It is usually seen either chained to the ground, being chased by Principal Barrage's "cleaner freaks", or crawling through the school vents. In "28 Sneezes Later", it's revealed that the Tazelwurm is actually highly intelligent and knows about what happened on the day of the prank. He gave Lee a file containing all the information regarding the prank, and even information regarding Lee's own past which appears to be intertwined with the prank. It later helps Lee on numerous occasions, and has led to him calling 'Taz'. "Tazel Wurm" comes from a Bavarian mythical animal, theTatzelwurmwhich is supposed to have the front of a cat and the hind of a lizard with no hind legs.