Clementine is an energetic, highly observant eight-year-old girl in the third grade. She lives in an apartment building and struggles to sit still in school. She prefers to process the world through sketching and observation. Although she excels in math and art, she has difficulty in English class and constantly worries that she is the "hard kid" in her family.

Margaret is Clementine's neighbor and friend, older by about a year. She is organized and highly concerned with her appearance, boasting a meticulously tidy bedroom. Her desire for perfection often clashes with Clementine's messy, spontaneous nature.

Clementine's mother is a caring parent who works as an artist, choosing to wear messy overalls instead of formal business attire. She supports her daughter's unconventional way of thinking and actively encourages her artistic pursuits.

Bill manages the apartment building where the family lives. He is a practical but deeply empathetic parent who takes time to guide Clementine through strong emotions. He involves his daughter in problem-solving tasks, like dealing with the building's pigeon issue.

Clementine's three-year-old brother is considered the "easy kid" in the family. Though he is an ordinary toddler, Clementine refuses to call him by his real name. She refers to him exclusively by vegetable names like Broccoli, Radish, or Zucchini.

Susan is Margaret's mother, a woman who prioritizes neatness and conventional good behavior. She wears traditional professional clothing and views Clementine's eccentricities as a negative influence on her daughter.

Principal Rice is the head of Clementine's school and frequently manages the young girl's behavioral issues. She attempts to enforce standard classroom rules, like sitting still and paying attention, but often finds herself confused by Clementine's conversational tangents.

Mrs. Jacobi is an older tenant in the apartment building. She unknowingly contributes to the building's pigeon problem by tossing snacks out her front window. Clementine regularly runs store errands for her.

Mitchell is Margaret's brother. He lives in the same apartment building and is part of Margaret's structured, organized household.

Amanda-Lee is another student at the elementary school. She serves as an alternative playmate for Margaret whenever Margaret and Clementine are arguing.

Alan is Margaret's mother's "special friend," a term Clementine understands as the adult word for a boyfriend. He dates Susan and spends time with her outside the apartment building.

Polka Dottie is Clementine's deceased pet cat. Clementine deeply misses her and creates a giant picture of her to help scare the pigeons away from the apartment building.

Mascara is Margaret's pet cat. Her presence makes Clementine feel sad, as she serves as a reminder of Clementine's own deceased cat.