Russell is a witty, mischievous fifteen-year-old living on a farm in rural Indiana in 1904. Viewing school as a useless prison, he dreams of running away to the Dakotas to work on a modern threshing crew and become an independent man. He relies on humor and practical farm skills rather than formal education, often clashing with his older sister when she assumes an unexpected position of authority.

Tansy is Russell and Lloyd's seventeen-year-old sister who typically attends high school in town. Described by her brother as countrified and bossy, she possesses a strong sense of responsibility and ambition. When the local school board considers closing the rural schoolhouse, she steps up to become the new teacher, determined to force her younger brothers to secure their futures through education.

Charlie is the strong, older son of the local Methodist preacher and Russell's best friend. Despite his age, he has not passed his eighth-grade examinations. He frequently joins Russell in plotting mischief and dodging schoolwork, though he surprisingly begins paying more attention to his grooming and behavior once Tansy becomes the teacher.

Glenn is a tough, capable nineteen-year-old from the socially isolated and run-down Tarbox family farm. Defying his family's dismissive attitude toward education, he makes the independent choice to attend school to better himself, proving to be surprisingly adept at natural science and practical skills.

Lloyd is Russell's sensitive, ten-year-old younger brother. Having lost his mother during his birth, he is closely looked after by his family. He genuinely enjoys farm work and life in the country, standing in contrast to Russell's restless desire to leave, and is highly perceptive of the family's social dynamics.

O.C. Culver is a widower and diversified farmer who raises cattle, hogs, and corn. As a member of the school board, he holds a respected position in the community. He models integrity for his children, guiding them gently and allowing them to learn from their own choices rather than interfering directly.

Aunt Maud is the deceased Mrs. Culver's sister, a nervous spinster who visits the farm daily to cook and care for the children. She holds a deep suspicion of modern inventions like the automobile and strongly prefers her quiet, traditional country life. She frequently worries about her own health and mortality.

Eugene is a dashing, ambitious representative for the Overland Automobile Company. Wearing motoring goggles and driving gloves, he embodies the encroaching twentieth century and modern city life. He travels the countryside promoting mechanization to farmers while simultaneously courting Tansy.

Aunt Fanny is an elderly, crotchety, and fiercely frugal community matriarch who owns the sugarbush grove near the school. Despite her terrible eyesight and intimidating threats toward trespassing students, she wields significant influence in the community and tests Tansy's new authority.

Miss Myrt was the longtime, deeply unpopular teacher at Hominy Ridge School. Known for her reliance on corporal punishment and a rigid approach to rote learning, her harsh methods alienated her students and made her an outsider in the community for over two decades.

Preacher Parr is the local Methodist minister and Charlie's father. He holds strict, old-fashioned views on education and morality, firmly believing in corporal punishment and viewing the modern generation of youths as degraded and lazy.

Known affectionately as "Little Britches," Beulah is a tiny, six-year-old girl starting her first year of school. Initially fearful and prone to tears, she quickly proves to be one of the brightest and quickest learners in the classroom when approached with gentle encouragement.

Lester is a quiet, puny bookworm around Lloyd's age who wears a distinct Buster Brown collar. Despite his small stature, he is the most advanced reader in the class and benefits from the close-knit nature of the small rural school, which protects him from bullying.

Nicknamed "Flopears," Floyd is a quiet student from a disadvantaged background who struggles to read. Often underestimated by the community, he possesses a hidden talent for observation and professional-quality art, quietly sketching his classmates and school events.

Pearl is an eleven or twelve-year-old girl entering a troublesome, rebellious age. Wearing a giant hairbow, she brings a sassy and impudent attitude to the classroom, frequently challenging Tansy's authority and acting disdainfully toward the younger children.

Mrs. Tarbox is the matriarch of an impoverished, socially ostracized family. Living on a neglected farm, she speaks with a heavy accent and outright refuses to send her children to school, demonstrating a profound lack of interest in their futures or education.

Mr. Whipple is the county superintendent of schools. He visits Hominy Ridge School to formally examine Tansy's competence as an educator and the academic progress of her pupils to determine if she deserves a provisional teaching certificate.

Mr. Owen is the younger assistant to Superintendent Whipple. During the official examination of the school, he takes a noticeable liking to Tansy and enthusiastically praises her students' correct answers.

Mr. Keating is the local mailman who drives a mail wagon on a rural delivery route. He proves helpful in a crisis when he uses his horse and wagon to pull Aunt Fanny out of a muddy ditch near the school.

J.W., short for "Just Worthless," is Russell's beloved pet dog. Despite his self-deprecating name, he is a loyal companion who constantly accompanies the boys on their rural adventures until a run-in with a porcupine threatens his life.