Donovan is a 13-year-old average student who struggles with impulse control and frequently pulls pranks. After his reckless actions severely damage the Hardcastle Middle School gymnasium, a clerical error inexplicably transfers him to the Academy for Scholastic Distinction (ASD). Although he lacks the raw intelligence of his new peers, he uses his video game reflexes and social awareness to survive. He quickly becomes the driver for the class robotics team, hoping to avoid detection while his family manages stressful times at home.

Dr. Shultz is the superintendent of the Hardcastle School District who operates under a strict policy of allowing absolutely no mistakes. He briefly catches the student responsible for the gym damage but immediately loses the slip of paper bearing the boy's name. This single moment of carelessness drives him into an obsessive, district-wide search to track down the culprit and exact punishment.

Chloe is a student at the gifted academy with an IQ of 159. She desperately wants to experience a typical middle school life, including dances, parties, and regular social interactions. She views Donovan's arrival as a fascinating introduction to the outside world, valuing his practical problem-solving skills over raw academic intelligence.

Noah is a student with a staggering IQ of 206, the highest in the academy. He experiences his extreme intelligence as a heavy burden, as teachers and parents constantly pressure him to live up to his potential. He is fascinated by YouTube and Donovan because both represent unpredictability and chaos, giving him hope that he might one day be capable of making a genuine mistake.

Katie is Donovan's 26-year-old sister who is experiencing her first pregnancy. With her husband serving in the Marine Corps in Afghanistan, she moves back in with her parents. Initially dismissive of the gifted students, she reluctantly allows them to study her pregnancy for class credit, eventually forming a genuine bond with the enthusiastic teenagers.

Mr. Osborne is the robotics and homeroom teacher at the Academy for Scholastic Distinction. He quickly realizes that Donovan lacks traditional gifted abilities, but he sees how the new boy unifies his highly regimented students into a cohesive team. He acts as a supportive mentor, trying to protect the students' extracurricular interests while fulfilling administrative mandates.

Ms. Bevelaqua is a strict math teacher at the academy who immediately suspects Donovan is an imposter. She places immense value on standardized test scores and traditional measures of intellect. Convinced that his presence dilutes the quality of the program, she makes it her personal mission to uncover the truth behind his enrollment.

Abigail is a relentlessly driven academy student whose entire life revolves around academic achievement and building an impressive college resume. She openly complains that Donovan's presence lowers the school's standards and treats his lack of intelligence as a personal insult, even while benefiting from his practical skills in robotics.

Daniel is one of Donovan's longtime friends from Hardcastle Middle School. He enjoys pulling pranks, mocking authority, and causing general chaos. He views the academy students as nerds and constantly pressures Donovan to revert to his old, impulsive habits for entertainment.

Daniel is Donovan's other best friend at Hardcastle. Like Nussbaum, he fails to understand Donovan's personal growth and actively mocks the gifted students. He tries to force Donovan into choosing between his old rebellious life and his new academic peers.

Tin Man is the highly advanced robot built by the academy's robotics class for an upcoming competition. Initially treated strictly as hardware by the gifted students, the machine takes on a new identity and unifying role once Donovan gives it a name and becomes its primary driver.

Mr. Del Rio is the principal of the Academy for Scholastic Distinction. He places absolute faith in the district's selection and testing processes. He firmly insists that a mistake in admissions is impossible, setting the stage for Donovan to remain undetected for an extended period.

Brad is Katie's husband, currently serving a combat tour with the Marine Corps in Afghanistan. His absence places emotional strain on Katie and the entire Curtis family, making his letters and his dog Beatrice their only connections to him during his dangerous deployment.

Beatrice is Brad's beloved dog. While he is deployed, she becomes lethargic and refuses to eat, deeply worrying the family. She bonds exclusively with Donovan, relying on him for hand-feeding and care while they try to understand the source of her condition.

Cynthia is Dr. Shultz's secretary at the Hardcastle School District. She unwittingly sets the entire plot in motion when she takes a scrap of paper from the superintendent's desk and processes Donovan's transfer to the academy, assuming it is an official administrative directive.

James is Donovan's ancestor who miraculously survived the sinking of the Titanic in 1912. Donovan frequently recalls his story during moments of stress, using James's unlikely survival against impossible odds as a source of inspiration to endure his own daily struggles.