Karen is a 28-year-old woman who co-founded and runs the Wright-Dobie School for girls. She is a practical educator who tries to understand her students' behavior logically rather than jumping to harsh punishments. She balances her career ambitions with her upcoming marriage to Dr. Joseph Cardin, maintaining a calm demeanor when dealing with difficult situations.

Martha is a nervous, high-strung woman around 28 years old who co-founded the Wright-Dobie School. She was raised by her dramatic aunt, Mrs. Lily Mortar, whom she now supports financially but struggles to tolerate in the school environment. She is highly emotional and harbors a strong, almost protective jealousy regarding her friendship with Karen.

Mary is a fourteen-year-old student at the Wright-Dobie School who maintains a sullen, dissatisfied expression. Raised and spoiled by her wealthy grandmother, she utilizes elaborate lies, feigned illnesses, and physical intimidation to manipulate everyone around her. She shows a distinct lack of empathy and treats any form of discipline as a personal attack to be avenged.

Mrs. Mortar is Martha's plump, 45-year-old aunt and a former actress who resides at the Wright-Dobie School. She relies entirely on her niece for financial support but contributes very little to the actual education of the girls, preferring to boast about her past stage offers. She is easily flattered and prone to making thoughtless, inflammatory remarks when she feels slighted.

Mrs. Tilford is a dignified woman in her sixties who holds significant social and financial power in the local community. She is deeply devoted to her granddaughter, Mary, whom she indulges and protects at all costs. Her fierce protective instincts make her highly susceptible to the girl's dramatic fabrications.

Joe is a relaxed, carelessly dressed physician around thirty-five years old. He hopes to marry Karen soon, despite the subtle resistance he receives from her co-headmistress. As Mary's cousin, he is familiar with the girl's spoiled nature and easily dismisses her dramatic medical complaints.

Rosalie is a plump student at the school who wears glasses and generally gets along with her peers. She harbors secret guilt over borrowing another student's bracelet without asking, which makes her extremely vulnerable to blackmail. She is fearful of authority and easily intimidated by stronger personalities.

Peggy is a student at the Wright-Dobie School who comes from a less wealthy background than her peers, saving her meager allowance for a bicycle. She is generally obedient and respectful of her teachers, but she falls under Mary's domineering influence and caves under physical or emotional pressure.

Evelyn is a young student with a pronounced lisp who struggles with basic tasks like sewing. She is naturally timid, deeply fearful of getting into trouble, and easily coerced into breaking the rules by her manipulative classmate.

Agatha is Mrs. Tilford's sharp-faced maid who has worked for the family for a very long time. Having observed Mary for years, she views the girl with clear-eyed skepticism and does not buy into the child's dramatic fabrications.

Helen is a student at the Wright-Dobie School. She is primarily concerned with locating her missing bracelet, a situation that inadvertently provides leverage for blackmail among the other girls.

Lois is a student at the school who focuses closely on her academic performance, continuing to rehearse her Latin even as the other girls engage in gossip or leave the room.