Mr. Kermit is a 55-year-old middle school teacher who has spent the last 27 years emotionally detached from his profession following a devastating cheating scandal. With only one year left until he qualifies for early retirement, he is assigned to room 117 as a deliberate ploy by the district superintendent to force him out. He initially plans to ignore his students and run out the clock, masking his former passion for education behind a gruff exterior.

Kiana is an eighth-grade girl temporarily staying in Greenwich while her mother shoots a movie out of state. Because she expects to leave in a few months, she adopts a short-timer attitude and decides not to correct the school administration when she is accidentally placed in the Unteachables class. She is observant and academically capable, initially viewing her eccentric peers from an emotional distance.

Parker is a fourteen-year-old farmer who holds a valid driver's license to help transport his family's agricultural goods. He struggles with severe dyslexia, which scrambles the letters he tries to read, causing him to feel completely inadequate in a traditional academic setting. Despite his reading difficulties, he possesses high mechanical intelligence and a deep well of empathy for those around him.

Dr. Thaddeus is the superintendent of the Greenwich school district and the primary adversary to Mr. Kermit. He was the principal during the cheating scandal 27 years ago and remains obsessed with preserving the school district's public image. He actively searches for bureaucratic loopholes to fire Mr. Kermit before the educator can claim his early retirement pension.

Aldo is an eighth-grade student who struggles with severe anger management issues. He experiences his rage as a physical heat and pressure, often lashing out destructively over minor provocations. Because administrators deem him too disruptive for mainstream classes, he has been relegated to room 117 without receiving the emotional support he needs.

Mateo is a highly observant student in the Unteachables class who interprets the real world entirely through the lens of television and movies. He assigns pop-culture character equivalents to everyone he meets, comparing himself to a mix of Bilbo Baggins and Spock. His nerdy demeanor and unique way of processing information make him a target for bullies and a misfit in the eyes of the school administration.

Barnstorm is a formerly celebrated star athlete at Greenwich Middle School who previously coasted through his academics on athletic merit. After sustaining a severe knee injury, he lost his utility to the sports teams and was subsequently placed in the Unteachables class. He has difficulty forging an identity outside of athletics and resents the sudden loss of his popular status.

Ms. Fountain is the upbeat, enthusiastic teacher in the classroom next to room 117. She utilizes methods typically reserved for younger students, such as positive behavior charts and circle time, to engage her middle schoolers. As the daughter of Mr. Kermit's former fiancée, her physical resemblance to her mother serves as a constant, uncomfortable reminder to him of his past.

Jake is a successful local businessman and the owner of Terranova Motors. Twenty-seven years ago, he was the enterprising student responsible for the cheating scandal that ruined Mr. Kermit's career. Now a wealthy adult, he maintains a smooth, sales-oriented persona but harbors intense guilt over the lasting damage his past actions caused his former teacher.

Elaine is a tall, physically imposing eighth-grade girl in the Unteachables class. Because of her deep voice and solid build, wild rumors circulate about her supposed violent history, causing both students and teachers to fear her. In reality, her intimidating reputation is entirely fabricated, though she allows the rumors to persist as a defense mechanism.

Stepmonster is Kiana's harried stepmother, who is tasked with caring for Kiana and an infant stepbrother while Kiana's mother works out of state. Overwhelmed by her responsibilities, she fails to properly register Kiana for school but attempts to maintain a supportive environment at home despite Kiana's initial resentment.

Grams is Parker's elderly grandmother who suffers from cognitive decline. She frequently forgets Parker's name, casually calling him kiddo, which secretly pains him. Despite her memory issues, she deeply loves her grandson and relies entirely on him for daily transportation and care.

Mrs. Vargas is the principal of Greenwich Middle School. Having known Mr. Kermit since the beginning of his career, she remembers the dedicated educator he once was. While she initially clashes with him over school policies, she serves as a foil to Dr. Thaddeus by prioritizing actual student progress over district optics.

Rahim is a student in room 117 who suffers from chronic exhaustion. Because his father's band rehearses at their house late into the night, Rahim is unable to sleep at home and frequently naps during school hours. His extreme lethargy led the administration to label him unteachable, while ignoring his strong artistic talents.