Mark is an intelligent, wealthy fifth-grade boy whose family constantly moves due to his parents' business ventures. Initially sullen and resistant to his new life in Whitson, New Hampshire, he views his stay as temporary and avoids engaging with his peers and teachers. However, he soon discovers a profound connection to the surrounding wilderness, immersing himself in outdoor survival skills that foster his independence.

Mr. Maxwell is the burly, nature-loving fifth-grade science teacher at Hardy Elementary School. He lives a modest, environmentally conscious lifestyle in a log cabin and takes great pride in leading the school's yearly week-long excursion. Despite his passion for teaching, he harbors strong biases against wealthy individuals, causing him to instantly misjudge Mark as a lazy, spoiled child.

Anya is a Russian immigrant who works as a live-in child caretaker for the Chelmsley family. She is highly attentive to Mark's daily needs, always ensuring he is well-fed with his favorite meals. Though she worries about his safety when he undertakes outdoor challenges, she allows him the space needed to mature.

Leon is a Russian immigrant and live-in caretaker for Mark, balancing Anya's cautiousness with a more adventurous spirit. Preferring the rugged, cold environment of New Hampshire, he acts as a positive male role model for Mark. He teaches Mark essential wilderness skills, such as snowshoeing and building campfires, fostering the boy's growing independence.

Jason is a fifth-grade student at Hardy Elementary and the first person to make Mark feel genuinely welcome. He brings out Mark's carefree, childlike side during the school's camping trip, engaging in lighthearted competitions like gathering firewood. His decision to bring a prohibited item on the trip inadvertently triggers a central conflict.

Mark's mother is a highly successful businesswoman who spends the vast majority of her time traveling for work. Though her demanding career keeps her away from home, she is deeply connected to Mark's sense of comfort and safety. She feels guilty about her frequent absences but prioritizes her corporate responsibilities.

Mark's father is a wealthy corporate owner who frequently relocates his family upon purchasing new companies. He is a distant but highly influential figure in Mark's life, prioritizing strength and adaptability. He takes great pride in observing his son develop independence and resilience in new environments.

Mrs. Stearn is a teacher at Hardy Elementary who serves as a chaperone for the fifth-grade excursion. She approaches the week-long camping trip with visible excitement and enthusiasm, supporting the students' outdoor education.

Mrs. Leghorn is a teacher at Hardy Elementary participating as a chaperone for the annual woods excursion. Unlike her colleagues, she appears anxious about the wilderness trip, though she remains attentive to the students' whereabouts.

Mr. Frost is a chaperone assigned to the Raven's Nest cabin during the school's camping trip. He establishes the ground rules for the students, ensuring they keep their belongings organized and ask permission before exploring the grounds.

The ranger is an unnamed park official working at Gray's Notch State Park during the school excursion. Unclouded by the teachers' biases, he provides an objective perspective on student behavior. He quickly identifies the true owner of a controversial multitool, forcing a moment of realization for the school staff.