Jessie is a gifted young girl who has completed second grade and is moving into fourth grade. She excels academically but has difficulty understanding social cues and making friends. Jessie uses reading as a coping mechanism and gradually learns to express her emotions better throughout the novel.

Mrs. Treski is the single mother of Evan and Jessie, working from home in a business role. She supports and challenges her children, striving to balance her work and parental responsibilities. Despite some lapses in attention, she aims to spend meaningful time with her children.

Megan is Evan's classmate and a new friend of Jessie. Together, they sell lemonade as summer ends. Megan is supportive, encouraging Jessie's self-esteem, and is generous, intending to donate lemonade earnings to charity.

Scott is a mean boy in Evan's class who antagonizes him and Jessie. He initially works with Evan for a day but remains a negative influence, culminating in stealing their lemonade money.