Bradley is the oldest and toughest student in Mrs. Ebbel's fifth-grade class, having repeated the fourth grade. He actively maintains a highly antagonistic "monster" persona at school, refusing to do homework and extorting his peers for lunch money. In the privacy of his bedroom, however, he cares for a large collection of toy animals and displays a vivid imagination. He frequently lies to his parents and teachers to avoid dealing with his academic and social struggles.

Carla is the newly hired counselor at Red Hill School. She stands out from the other staff with her casual attire, such as a "Rock 'n' Roll" t-shirt, and her highly disorganized office. She adopts a philosophical, non-directive approach to counseling, encouraging her students to think for themselves rather than giving them strict rules to follow.

Jeff is a new transfer student who is seated next to the outcast Bradley Chalkers due to a lack of available desks. Polite and slightly timid, he attempts to befriend Bradley, even paying him a dollar to prevent Bradley from spitting on him. He quickly gains attention from other students after accidentally wandering into the girls' bathroom.

Colleen is a fifth-grade girl who shares a close-knit friend group with Melinda and Lori. She develops an immediate crush on the new student, Jeff, and desperately wants to invite him to her upcoming birthday party. She often seeks advice to handle her social dilemmas, though her parents strictly oppose her speaking with the school counselor.

Melinda is a strong, assertive fifth-grade girl who fiercely defends her friends. She acts as the enforcer of her social trio and refuses to be intimidated by the rough-acting boys in her class. She directly challenges Bradley's attempts to bully her group.

Lori is a highly energetic fifth-grade girl who acts as a vocal sidekick to Colleen and Melinda. She is outspoken, frequently bombards people with rapid-fire hellos, and heavily invests herself in the social dynamics of her friend group.

Janet is Bradley's mother. She frequently tries to protect him from his father's strict discipline while also struggling to manage his behavioral issues. She attends school conferences to advocate for her son, maintaining the belief that he is secretly a good person despite the overwhelming complaints from his teachers.

Bradley's Dad is a stern police officer. He works a desk job at the department due to a previous gunshot wound to his leg. He acts as the primary disciplinarian in the household, openly calling out Bradley's lies and refusing to tolerate misbehavior.

Claudia is Bradley's older sister by four years. She frequently antagonizes him and laughs at his mistakes. Despite their constant bickering, she shows flashes of sibling solidarity, such as buying him a toy bear to replace one she accidentally damaged.

Mrs. Ebbel is Bradley's overwhelmed fifth-grade teacher. Managing a classroom of 29 students, she has largely given up on reforming Bradley's behavior and admits she would prefer if he sat in the closet. She is the first adult to recommend that Bradley see the new school counselor.

Ronnie the Rabbit is one of Bradley's approximately twenty toy animals. In Bradley's vivid imagination, she has a distinct personality, speaks to him regularly, and acts as a comforting presence when he feels rejected by the human world.

Bartholomew is a toy bear gifted to Bradley by his older sister. He serves as a voice of reason and loyalty within Bradley's imaginary animal community, frequently participating in dramatic missions.

Robbie is a fifth-grade boy who plays basketball at recess. He holds a negative view of Bradley and questions why the new student, Jeff, spends time with him.