Marlee is a twelve-year-old math prodigy who counts the words she speaks each day due to her extreme shyness. Living in Little Rock in 1958, she prefers the predictability of prime numbers over human interactions. She categorizes people by beverages to understand them better and relates easily to the lions at the local zoo, wishing she could roar like them.

Liz is a confident new student who quickly identifies Marlee's love for math and initiates a friendship. She is bold and outspoken, providing a direct contrast to Marlee's quiet nature. She uses math puzzles called magic squares to connect with Marlee and encourages her to practice speaking aloud at the zoo.

Mr. Nisbett is an English teacher and Marlee's father. Marlee compares his calming presence to a comforting glass of milk. He holds progressive views regarding school integration but struggles to make his voice heard in a heavily segregated community. He seeks to shield his family while maintaining his personal principles.

Marlee's mother is a practical woman whom her daughter likens to hot black tea. She initially opposes integration out of a desire to maintain social order and protect her family from retaliation. She struggles to communicate effectively with her youngest daughter.

Red is JT's older brother and the embodiment of virulent prejudice in the community. He is an aggressive bully who actively intimidates anyone attempting to cross the color line. He relies on physical threats and vandalism to enforce his segregationist worldview.

Judy is Marlee's older sister, described by Marlee as an ice-cold Coca-Cola. She is a high school student directly affected by the governor's decision to close the schools. She acts as a protective force for Marlee but frequently gets wrapped up in her own teenage concerns.

David is Marlee's older brother who studies engineering at a university. Marlee likens his warm personality to sweet iced tea. He recognizes his younger sister's extraordinary math abilities and actively encourages her academic interests.

Betty Jean is the African American maid hired by the Nisbett family. She is an insightful woman who gradually opens Marlee's eyes to the realities of living in the segregated South. The two form a quiet bond over shared chores and tea.

James-Thomas, known as JT, is the popular heartthrob at Marlee's school. He uses his looks and charm to mask his academic shortcomings, manipulating Marlee into doing his math homework. He is heavily intimidated by his older brother and struggles to form his own moral compass.

Sally is Marlee's first school friend. She is bossy, highly concerned with appearances, and strongly influenced by her family's prejudices. She is often insensitive to Marlee's feelings but remains a constant presence in her daily routine.

Little Jimmy is a quiet classmate who struggles to speak his mind. He channels his unsaid thoughts into a personal journal. He harbors a crush on Marlee and proves to be an understanding peer.

Pastor George is an African American minister and a prominent figure in his community. He takes on leadership roles to advocate for civil rights. He is cautious about the dangers of interracial alliances but acts as a bridge between groups.

Curtis is Betty Jean's son. He is unjustly accused of egging a house simply because he is an African American boy near the scene of a crime, demonstrating the systemic bias of the local police.

Mr. Dalton is a local figure and the father of JT and Red. He fosters a household environment rooted in prejudice and intimidation. He is bad-tempered and rules his family through fear.

Mrs. Dalton is the timid mother of JT and Red. She lives in fear of her domineering husband. Despite her anxiety, she quietly seeks to counteract his hateful actions by joining an integrationist women's committee.

Mr. Fullerton is Liz's father. He agreed to enroll his daughter in a white school to afford her better opportunities. He works to protect his family in a deeply hostile environment.

Mrs. Fullerton is Liz's mother. She is highly protective of her children and actively discourages Liz from associating with Marlee, fully understanding the severe physical dangers such a friendship poses.

Miss Winthrop is Marlee's Sunday school teacher and a dedicated member of a local women's committee. She is an active organizer who mentors Marlee in petitioning and civic engagement.

Mr. Harding is Marlee's math teacher. Recognizing her advanced aptitude, he provides her a quiet place to eat and challenges her with algebra. He encourages her to view life's complex problems through mathematical frameworks.

Tommy is Liz's younger brother. He frequently accompanies his older sister around town and relies on her protection in their community.

Granny is Mr. Nisbett's mother. She provides a safe haven for Judy when the Little Rock high schools close, ensuring her granddaughter can continue her education without interruption.