Maureen is a highly intelligent, academically gifted sixth-grader who thrives on routine and familiarity. Known within her family as "the thinker," she struggles with severe social anxiety and low self-confidence, often relying on her identical twin sister to speak for her in public settings. Her forced enrollment in Cadet Corps and separate classes pushes her out of her comfort zone, forcing her to figure out who she is as an individual.

Francine is Maureen's identical twin sister, older by exactly two minutes. Naturally outgoing and a talented public speaker, she is affectionately known as "the talker" of the family. Seeking her own identity away from simply being a "Carter twin," she actively changes her wardrobe and adopts the nickname "Fran" to establish her independence.

The twins' mother is a loving and responsible parent who wants the best for her daughters. She sets strict boundaries to help them develop into good people, though she sometimes makes parenting mistakes by keeping secrets about their school arrangements. She is fiercely protective of her children.

The twins' father is deeply invested in his daughters' growth and development. He occasionally keeps secrets—such as the true reason for Maureen's class schedule—in a misguided attempt to help them build confidence. He is reflective about his parenting and willing to admit when his strategies cause unnecessary tension.

Curtis is Maureen and Francine's older half-brother who recently graduated college and works as a first-grade teacher. Living in his own apartment, he maintains a close connection with his family. He acts as a grounded mentor figure to his younger sisters, offering them a mature perspective on their changing relationship.

Monique is a sixth-grader who became inseparable from Maureen in the third grade. She acts as the social glue for their broader friend group. As middle school begins, she tries to maintain her friendships with both twins, even when their personal rivalry threatens to split their social circle.

Nikki is a long-time friend of the twins, having known them since kindergarten. She enjoys going to the mall but faces a harsh reality when a shop attendant racially profiles her and her friends. She relies on her mother to help stand up against the injustice.

Tasha is part of the twins' core friend group from elementary school. Along with Nikki, she enjoys mall trips but finds herself managing the shifting social dynamics of middle school, eventually spending more time with new band friends while trying to remain neutral in the twins' dispute.

Amber is a diligent and highly organized sixth-grader who excels in Cadet Corps. She is quick to offer support and becomes one of Maureen's first new friends in middle school, eventually helping manage Maureen's school campaigns and pushing her peers to succeed.

Richard is a creative and artistic sixth-grader in Cadet Corps. He struggles to pay attention in class and is frequently punished with push-ups, but he is fiercely loyal and eager to help his friends. He plays a key role in designing campaign materials for Maureen.

Bryce is a confident seventh-grader and the student leader of the Cadet Corps class. He provides a kind, encouraging counterbalance to the teacher's strictness, helping struggling sixth-graders master their drills. He serves as Maureen's primary middle-school crush.

Master Sergeant Fields is an intense, strict former Army officer who teaches Cadet Corps. She pushes her students hard but genuinely wants to build their self-esteem, even offering Maureen a unique extra credit opportunity to coax her into developing better leadership skills.