Joey is a 10-year-old boy experiencing severe hyperactivity and impulsivity that makes it difficult for him to focus or sit still. After his parents leave when he is in kindergarten, he lives with his paternal grandmother until his mother eventually returns. He is exceptionally energetic and naturally kindhearted, though his inability to control his actions frequently lands him in the principal's office or the school nurse's care. He longs for stability and clearly understands that his brain works differently than those of his peers.

Fran is Joey's biological mother who works at a local beauty parlor. She leaves the family when Joey is in kindergarten but eventually returns to take responsibility for his care, pushing his grandmother out of the house in the process. She is determined to establish strict rules for Joey and closely monitors his medication, though she carries heavy guilt regarding her past alcohol use and her long absence from her son's life.

Joey's paternal grandmother raises him alone after his parents depart, running a chaotic household littered with unfinished projects and newspapers covering the beds. She shares the family trait of being "wired" and often administers erratic, inappropriate punishments to Joey when she is overwhelmed. Despite her harsh methods, she shares moments of playful energy with her grandson before eventually moving out.

Mrs. Maxy is Joey's primary school teacher. She reads his file and genuinely tries to accommodate his need for physical activity by giving him tasks like sharpening pencils. However, her patience often wears thin when his uncontrollable energy creates disturbances or dangerous situations in the classroom.

Ed Vanness, frequently referred to as Special Ed, is a tall caseworker at the Special Education Center whose primary goal is to help students rather than punish them. He speaks calmly to Joey, reviewing his past mistakes without judgment to help the boy learn better decision-making skills. He recognizes that Joey's chaotic home life contributes significantly to his behavioral struggles.

Doctor Preston is a medical professional who evaluates Joey to rule out bodily dysfunctions affecting his behavior. He takes a comprehensive approach to Joey's care, ordering specific tests like a brain scan and discussing the intersection of medical and behavioral problems with Joey and his mother.

Carter is Joey's biological father who absconds when Joey is young and relocates to Pittsburgh. He shares the hyperactive traits of his mother and son, and his history of alcohol abuse makes Fran hesitant to allow him back into Joey's life.

Principal Jarzab is the head administrator at Joey's school. She frequently interacts with him following his classroom ejections, reviewing his behavior goals and ultimately managing his disciplinary track when his impulsivity causes harm.

Maria is the class president in Mrs. Maxy's room and often acts as a peer monitor. She becomes heavily involved in Joey's disciplinary trajectory when a collision between them results in a severe physical injury to her face.

Seth is an opportunistic classmate who easily recognizes Joey's gullibility. He encourages Joey's worst impulses for his own amusement, offering him money to swallow a key and tricking him into asking for flies on his pie during a field trip.

Nurse Holyfield works at the school clinic and is highly familiar with Joey due to his frequent accidents. She asks him pointed questions about his medication routine and home life, trying to find the root cause of his erratic symptoms.

Mrs. Howard runs the Special Education room at Joey's primary school. She manages students with severe disabilities and uses physical restraint tools, such as heavy chairs and rabbit slippers, to prevent hyperactive children from causing disturbances.

Harold is a physically disabled student who wears a neck brace and uses a wheelchair. His inability to perform simple tasks, like blowing out a birthday candle, elicits strong sympathy from Joey, who impulsively attempts to help him.

Charlie is a young boy with small, deformed arms who shares the bus route with Joey. He is exceptionally friendly and outgoing, immediately introducing himself and attempting to shake hands, which helps ease Joey's intense anxiety about the new school.

Mr. Dombrowski is Maria's large and fiercely protective father. Following his daughter's injury at school, he harbors immense anger toward Joey and his mother, explicitly threatening the boy to ensure he stays away from his family.

Pablo is a Chihuahua-dachshund mix puppy that Joey dreams of bringing home to provide the reliable companionship he always wished for. For Joey, acquiring and training a dog represents a chance to heal from the pain of waiting by the window for his own absent parents.