Summer "Tinkerbell" Hathaway is a student at Horace Green Prep School and is a member of the class that Dewey Finn starts teaching as a substitute teacher under the name of Ned Schneebly. Summer is the class factotum. She played the clarinet in the school music class, and becomes the manager of Dewey's School of Rock band. Summer is well-educated, clever, responsible but sometimes sarcastic young girl. As the class factotum, she thinks mostly of succeeding and earning good grades. When Dewey gave her a role as the band's "groupie", she looked up the term and was displeased that she was to be what she compared to a slut. She threatened to tell her mother about her part in the "class project", and Dewey was forced to give her a more important role as the band's manager, which she accepts and takes seriously. Oddly, despite being smart and clever, she was easily tricked by Dewey to believe that they would be graded for the "class project".
After weeks of practice, Dewey sneaks Summer and the band out of school to the Battle of the Bands concert hall, where they were denied an audition for arriving late. Summer gives Dewey the idea of posing the students as orphans terminally ill of a fictitious disease. The ruse is a success, and their band gets listed.
After Dewey is exposed as a fraud posing as their teacher, several of the students are upset, and Summer is particularly displeased that they weren't being graded. But after a discussion with the class, everybody agrees that they enjoyed their time with Dewey as their teacher, and that they worked too hard for the band to give up on the concert. They sneak out of school and pick up Dewey. Dewey rejoins the class and apologizes for lying to them, but with no regrets, Summer simply urges that they would be late, and they proceed to the concert hall.
The band's performance is a great success, and the parents of the students, who were upset that their children were being taught by a fraud, lose all of their ill feelings after being greatly amazed by their children. Several concert executives who saw the School of Rock's performance are also impressed and wish to see the manager, and Summer introduces herself to them as the band's manager.
After the concert, the School of Rock becomes an after-school program, and Summer has taken on a full managerial tone and shoulders responsibility for the musical direction of the band. Summer was on the phone with more potential gigs opportunities and record deal offers for the band.