Maddie is a student in Room 13 who comes from a poor family, though she is better off than her classmate Wanda. She wears hand-me-down clothes that her mother disguises with new trim to avoid detection by the other children. She feels deep discomfort when her best friend initiates cruel games in the schoolyard. Her fear of becoming the next target of bullying keeps her entirely silent.

Wanda is a young Polish immigrant who lives with her father and brother in Boggins Heights, an impoverished and muddy part of a small Connecticut town. She wears the exact same faded blue dress to school every day, making her a frequent target for teasing from her peers. To cope with her social isolation, she relies on a rich imagination. She insists to the other girls that she owns a hundred beautiful dresses lined up in her closet at home.

Peggy is the most popular and affluent girl in Room 13. She is confident, successful at academics, and widely considered the best artist in her class. She leads the other children in the dresses game, mockingly interrogating Wanda about her wardrobe outside the school. She genuinely believes Wanda lacks the awareness to understand she is being insulted.

Jan is Wanda and Jake's father. As a Polish immigrant trying to provide for his family in early 20th-century America, he lives with his children in a small house in the run-down neighborhood of Boggins Heights. He is fiercely protective of his family and refuses to passively accept the xenophobia prevalent in their Connecticut town.

Jake is Wanda's brother who lives in the small house in Boggins Heights. As a Polish immigrant in a predominantly American-born town, he shares in his family's poverty and the social isolation that comes with their ethnic background.

Miss Mason is the teacher of Room 13 at the small-town Connecticut school. She organizes daily classroom activities, such as the morning recitation of the Gettysburg Address, and oversees the annual drawing contest. She acts as a serious moral authority for the students in her care.

Cecile is a student in Room 13 whose fashionable clothing inadvertently sparks the primary conflict in the schoolyard. When she arrives at school wearing a striking new red dress, the other girls gather around to admire it. This attention prompts Wanda to approach the group and make her own claims about her wardrobe.

Mr. Svenson is an older resident of the run-down Boggins Heights neighborhood. He is a local figure whom all the town's children find intimidating. His presence adds to the bleak and uninviting atmosphere of the impoverished area where the Petronski family resides.