Holling is a seventh-grade boy living in the "Perfect House" on Long Island in 1967. As a Presbyterian, he is the only student who does not attend religious classes on Wednesday afternoons, leaving him alone with his English teacher. He loves baseball, lunch recess, reading adventure stories, and quietly blending in. He feels intense pressure from his father to eventually take over the family architecture business.

Mrs. Baker is Holling's seventh-grade English teacher at Camillo Junior High. Though she initially appears rigid and unhappy about losing her free period, she possesses a deep love for literature, particularly Shakespeare. She hides her constant worry for her husband, who is deployed in Vietnam, behind a professional exterior. Her family also owns Baker Sporting Emporium, a prominent local business.

Mr. Hoodhood is the prominent owner of the architecture company Hoodhood and Associates. He expects his family to project a flawless image to the community, taking great pride in their "Perfect House." He views personal relationships primarily as business opportunities and demands absolute respect from his family.

Heather is Holling's older sister who attends the local high school. She embraces the counterculture of the late 1960s, listening to the Monkees and adopting "flower child" ideals. Her vocal opposition to the Vietnam War frequently puts her at odds with her conservative father.

Meryl Lee is a seventh-grade student and the daughter of a local architect. She is a close friend and romantic interest of Holling. As the daughter of Mr. Hoodhood's main business competitor, her loyalties are split between her family and her personal friendships.

Danny is one of Holling's seventh-grade classmates. He attends Hebrew school at Temple Beth-El on Wednesday afternoons and prepares for his upcoming bar mitzvah. He is fiercely loyal, deeply loves the New York Yankees, and demonstrates a strong sense of justice when defending his friends.

Doug is a mischievous seventh-grader in Holling's class who loves to cause trouble and test the teachers' patience. Despite his reputation as a prankster who collects items for his elaborate schemes, he becomes a solid part of Holling's loyal friend group.

Mai Thi is a Vietnamese refugee sponsored by the Catholic Relief Agency who joins Holling's seventh-grade class. She faces prejudice and bullying from some students and community members due to the ongoing war in her home country. Despite this hostility, she displays quiet courage and resilience.

Mrs. Bigio is the cafeteria worker at Camillo Junior High. She is married to a soldier fighting in the Vietnam War. She bakes treats for the school and local community events, but she struggles immensely with the personal toll of the war and directs her grief outward.

Mrs. Sidman is a staff member at Camillo Junior High with notoriously bad luck. After suffering a severe prank by Doug Swieteck the previous year, she moves to administrative roles, taking on more authority despite her constant anxiety about student misbehavior.

Mr. Guareschi is the strict principal of Camillo Junior High. Holling suspects him of having ambitions to become a dictator of a small country. He is rigid, obsessed with order, and insists that school remains open regardless of weather conditions.

Mr. Kowalski is Meryl Lee's father and the owner of Kowalski and Associates. His business struggles financially as he competes directly against Holling's father for major local contracts, including the new junior high school project.

Doug Swieteck's unnamed older brother is an intimidating eighth-grader at Camillo Junior High. He bullies the younger students and holds intense grudges. He goes out of his way to embarrass Holling by plastering humiliating photos of him across the school hallways.

Coach Quatrini is the demanding gym teacher and cross-country coach at Camillo Junior High. He pushes his students to their physical limits and emphasizes the importance of motivation, which he refers to as "The Big M."

Mr. Goldman is the owner of Goldman's Best Bakery and the director of the Long Island Shakespeare Company. He offers Holling a discount on baked goods in exchange for performing in his upcoming Holiday Extravaganza production.

Lieutenant Baker is Mrs. Baker's husband who is serving in the military overseas in the Vietnam War. His deployment causes significant distress for his wife, and his safety becomes a point of concern for the entire school community throughout the year.

Sycorax and Caliban are two gargantuan pet rats kept in Mrs. Baker's classroom. Gifted to her by her husband, they frequently escape into the walls and ceilings of the school. Their presence causes panic and provides Holling with unexpected athletic motivation.

Holling's mother is a quiet presence in the Hoodhood household. She maintains the family's image but generally defers to her husband's strict rules, rarely intervening in his disputes with their children.