Mac is an observant, precocious 11-year-old boy who values honesty above all else. He frequently questions authority figures who attempt to hide uncomfortable realities from children. He manages a complicated family life, spending time with his estranged father while relying heavily on his grandfather for guidance. When he discovers blacked-out words in his school reading assignment, his curiosity and sense of justice drive him to demand answers.

Marci is an intelligent, mature sixth-grader who strongly identifies as a feminist. She is quick to recognize systemic issues in her town and points out the sexist implications of the censorship in their classroom reading. She provides a grounded, confident presence for her friends.

Denis is Mac's anxious, sensitive best friend. He worries constantly about strict rules and getting in trouble, often fearing negative consequences from authority figures. Despite his anxieties, he remains loyal to his friends when they uncover altered texts in their literature circle.

Ms. Sett is a sixth-grade teacher and a staunch enforcer of her town's strict regulations. She frequently writes letters to the local newspaper advocating for conformity, curfews, and safety over personal freedoms. She believes she is protecting her students by altering their reading materials to remove language she finds inappropriate.

Mac's grandfather is a Vietnam War veteran who lives with his daughter and grandson. Having participated in countercultural protests in the past, he serves as a strong, reliable father figure to Mac. He uses meditation to process his own history while encouraging his grandson to question authority and express his emotions openly.

Mac's mother works in a hospice facility, demonstrating immense patience and kindness in her daily life. She serves as a calm, steadying force in her household. She carefully manages interactions with her estranged husband to maintain peace, setting an example of grace for her son.

Mike is Mac's estranged father, who has lived away from the family for several years. He exhibits erratic, unpredictable behavior and insists to his son that he is an alien anthropologist studying humans on Earth. He struggles to experience or communicate standard human emotions, causing confusion for his son.

Aaron is a sixth-grade classmate who initially displays ignorance and repeats close-minded beliefs. He often teases other students and acts out in class. His perspective is rooted in the same rigid worldview that governs the town, though he values his own personal freedoms.

Hoa is a sixth-grade student who participates in the literature circle with Mac, Marci, and Denis. She decides to drop her English name, Hannah, to honor her birth culture after being inspired by their reading material. She becomes a quiet but vital ally in uncovering the extent of the classroom censorship.

Dr. McKenny is the principal of the local school. She treats the students' concerns about intellectual freedom with condescension, downplaying the severity of the altered books. She prefers to maintain order and avoid conflict rather than address the core issue of censorship.

Jane Yolen is the real-life author of The Devil's Arithmetic. She acts as an inspirational figure for Mac, corresponding with him after he reaches out about the black rectangles covering words in her novel. She advocates strongly for children's right to read unvarnished truths.