Nick Allen—the main character, an inventive fifth grader at Lincoln Elementary School.

Miss Deaver—Nick's third-grade teacher, a new educator.

Manny—the custodian at Lincoln.

Mrs. Avery—Nick's hawk-nosed third-grade teacher.

Janet Fisk—Nick's friend, and a co-conspirator in the blackbird noises in fourth grade.

Mrs. Granger—Nick's nemesis, and the fifth-grade language arts teacher.

Mrs. Allen—Nick's mom.

James Allen—Nick's older brother. He is in college when Nick is in fifth grade.

John, Pete, Chris, and Dave—other fifth graders who Nick gets to spread the term "frindle."

Mrs. Margaret Chatham—principal of Lincoln Elementary, she is a large, firm woman.

Tom Allen—Nick's father.

Judy Morgan—reporter for The Westfield Gazette.

Ted Bell—sells ads for The Westfield Gazette. He passes the frindle story to Judy.

Mrs. Freed—the Lincoln Elementary School secretary.

Bud Lawrence—a local tycoon who helps spread the term "frindle."

Alice Lunderson—works for a television station in Betherly, a town near Westfield.

Nick (Nicholas) Allen is the novel's main character. He is mostly, but not completely, innocent and that contributes to his appeal. For the most part, he is simply an inventive boy who has ideas spilling out of him all the time. He is also a bit of a rebel, someone who tries to get things to go a little more his way than that system might allow. These traits combine to guide him in transforming his third grade classroom into a sandy tropical paradise…when it is winter in New Hampshire. They are also the reason he is the only one to notice that Mrs. Avery's nose looks like a hawk's beak. With his new knowledge about blackbirds and his apt comparison to Mrs. Avery’s nose, Nick fills the classroom with distracting—but entertaining—peeps.

Nick is an engaging character. He is fun. Anyone who remembers how dull elementary school can be will cheer his rebellion. However, much of the time his rebellion, while creative, is somewhat obvious. He is told to study—so he rebels. He is told to do an oral report—so he uses it to kill class time. His first strategy to life is a disruption, whether through reversing what he has been told or though carrying it out too emphatically. It is not until he interacts with the existing power structure—primarily Mrs. Granger, but also principal Chatham—that his interaction with the world grows more complex. He moves from a straightforward action and response pattern to fuller narratives and metaphors. He recognizes the scripted nature of his conflict with Mrs. Granger when he sees them as two generals meeting under a flag of truce, and he sees that he is only one player in a complex battle when he sees the clash between Mrs. Chatham and his mother when Chatham comes to visit their home. These lead him to a growing complexity and richness of character, one that is underscored at the end of the novel through Nick’s appreciative gifts for Mrs. Granger.

Mrs. Lorelei Granger's reputation precedes her but it does not exceed her. While she is not the giant she seems to be to the younger kids, and does not really have X-ray vision, she is in many ways larger than life. She holds herself to extremely rigorous standards of self-presentation (dressing sharply), professional performance (never missing a day of school, starting kids working right away), and, above all in academics, particularly the language use that she loves so much.

However, while she accents high performance, from her first appearance it is clear that she has a sense of humor, and that her mind is quite lively. This can be seen in how immediately she recognizes Nick's attempts to divert the class, rather than being taken in by them as other teachers are. In this, and in the role she chooses to play in Nick's frindle drama, one of the striking things about Mrs. Granger's character is that she recognizes that she is playing a role. The other teachers, and principal Chatham, all seem to forget this, and to blur the line between self and role. Mrs. Granger, while often strictly formal, still enables creativity and self-expression. She plays the role of Nick's enemy but she is really his necessary challenger. She helps Nick become great.