Suds is an anxious but well-meaning third-grader who desperately wants to earn the first halo prize for good behavior in his new class. Nicknamed for his habit of taking calming bubble baths, he struggles with perfectionism and a deep need for external validation. He treats the classroom reward system like a high-stakes race, often letting his competitive nature overshadow his genuine kindness.

Mrs. Simms is a compassionate third-grade teacher who prioritizes the moral and emotional development of her students. She introduces the halo reward system to encourage empathy and integrity, expressly rejecting bribery or superficial performative acts. She maintains a perceptive, authoritative presence in the classroom.

Suds's mother is a responsible, involved parent who understands her son's anxious disposition. She introduced the calming bubble baths that earned him his nickname and frequently acts as his primary confidante. She offers indirect advice to help him manage his social challenges and treat his sister better.

Amy is Suds's younger sister, currently in the second grade. Nicknamed "Zippernose" by her brother, she frequently engages in typical sibling rivalry and fights for their parents' attention. Her candid observations about Suds's need to always be first force him to reflect on his behavior.

Joey is a new student in Mrs. Simms's class who immediately establishes himself as a mischievous foil to Suds. He openly challenges the classroom dynamics, questions the halo competition, and looks forward to being a fourth-grade "rat." His blunt attitude creates significant social tension.

Judy is a third-grade student who has been the object of Suds's affection since the first grade. She consistently demonstrates a lack of interest in him and pays him no attention, even after his crush becomes public knowledge.

Constantina is a fellow third-grade student in Mrs. Simms's class. She experiences the same pressures of the halo reward system as the rest of her peers, serving as a quiet presence in the classroom as the intense competition unfolds.

Darren is a third-grade student who quickly becomes a source of stress for Suds. As the week progresses, Suds views Darren as his primary competition for the teacher's approval, driving his perfectionism to unhealthy levels.

Suds's father is a supportive presence in the Morton household. He participates in family dinners and offers his perspective on the events occurring in his son's classroom, adding to the family's discussions about school rules.