[citation needed] A feature film adaptation of the novel, directed by Julia Hart and starring Grace VanderWaal, was released in 2020 on Disney+.

[6] The book introduces its main character, Leo, at an early age, which is followed by his move from his home state of Pennsylvania to Arizona when he is 12.

Before the move, his Uncle Pete gives Leo a porcupine necktie as a farewell present, inspiring him to collect more like it.

Hillari Kimble, a well known and somewhat popular girl at Leo's school, declares that Stargirl is a fake, and speculation and rumors abound.

Though at first rejected by most of the students, Stargirl gains a measure of popularity and is asked to join the cheerleading squad after she succeeds in getting the crowd excited about the school's losing football team while cheering for them at a game.

Their anger comes to a head during the filming of the student-run television show, Hot Seat, which is run by Leo and his best friend Kevin.

She is shunned by the entire student body, except for her friend Dori Dilson, Leo, and, to some extent, Kevin.

They spend more and more time together, and Leo experiences her unusual lifestyle and starts helping her with various projects, such as leaving cards for people they don't know and dropping change on the sidewalk for others to find.

She starts going by her real name (Susan), wears typical teen clothing, and becomes obsessed with being accepted and popular.

She convinces the bandleader to play the "Bunny Hop," and the other students come to join her in the dance until the only people not in line are Hillari Kimble and her boyfriend, Wayne Parr.

Flashing forward fifteen years, a now-adult Leo notes that his former high school has become permanently changed, and wonders what has happened to Stargirl.

The film is directed by Julia Hart, from a screenplay written by Kristin Hahn and stars Grace VanderWaal in the title role.

While Kevin and Dori are included, with the former's last name changed from Quinlant to Singh to match with the actor's ethnicity, various new characters are added as part of Leo and Stargirl's social group.