Gene is a sixteen-year-old student from the South attending the Devon School in New England during the Summer Session of 1943. He pushes himself to achieve top grades and become class valedictorian. He conforms to the school's strict expectations and processes his surroundings through a lens of intense, unvoiced academic and social competition. He forms a secret jumping society with his charismatic roommate, harboring deep personal insecurities.

Phineas is the top athlete at the Devon School, possessing a natural grace and an effortless ability to win physical challenges. He wears a bright pink shirt and uses a school tie as a belt, confidently talking faculty members out of issuing punishments for his broken rules. He invents the game of blitzball and views his peers as friends rather than rivals, assuming his friends share his uncomplicated loyalty.

Brinker is a prominent student who commands numerous leadership positions in campus organizations and prefers politics to athletics. He adopts a pragmatic, highly patriotic attitude toward the ongoing war and frequently urges his classmates to prepare for enlistment. He operates with a strict sense of rules, accountability, and justice.

Elwin is a quiet student who collects biological specimens and sketches his environment rather than engaging in aggressive athletic training. He cross-country skis to search for beaver dams and maintains his own peaceful routine away from the fast-paced school culture. He holds a charter membership in the summer jumping society but hesitates to actually participate in the tree jumps.

A substitute teacher working at the Devon School during the summer session. He attempts to enforce the school's regulations regarding mandatory meals but operates with a generally lax attitude. He listens to cheerful, rambling explanations for bad behavior without issuing standard punishments.

The substitute headmaster of the Devon School for the summer. He teaches American History during the regular term. He hosts the traditional term tea for students and displays a willingness to laugh at absurd situations, prioritizing campus peace over strict discipline.

The wife of the summer substitute headmaster. She engages the students in polite conversation during social events, advocating for the protection of art and museums during military bombing campaigns.

A dedicated student at the Devon School who possesses a deep, genuine interest in learning. He plays the trumpet and tennis with noticeable ease. His tendency to get carried away by his academic interests sometimes distracts him from focusing solely on his final grades.

The campus doctor at the Devon School. He treats student injuries with a practical but highly sympathetic approach. He provides direct medical assessments and advises students on how to emotionally support injured peers during difficult recoveries.

The master in charge of Gene and Phineas's dormitory during the Winter Session. He represents the return of strict discipline and traditional Devon School rules after the relaxed summer. He firmly believes that all student athletic training should directly prepare young men for military service.

The manager of the Devon School crew team. He holds a superiority complex and clashes quickly with his peers. He plans to finish his education and enter specialized military training programs rather than enlisting immediately as a foot soldier.

Brinker's father, an older gentleman who holds highly romanticized, patriotic views of military service. He visits the school and expresses jealousy toward the young men who have the opportunity to fight for their country, expecting his son to choose a prestigious military branch.

Brinker Hadley's roommate at the Devon School. He follows Brinker's orders with absolute literalness, spending hours in freezing temperatures out of fear of abandoning his assigned post during winter activities.

The wrestling coach at the Devon School who holds training in first aid. He assists the campus doctor in moving and treating injured students safely.