Michelle Trachtenberg and Melora Hardin have joined the cast of "17," New Line's teen comedy starring Zac Efron.

Burr Steers is directing, while Adam Shankman and Jennifer Gibgot are producing via their Offspring.

In a scenario that turns the concept of "Big" on its head, the Jason Filardi-penned script follows a middle-age father who wakes up to find he's 17 again. In order to be close to his children, he enrolls in the same school as they attend.

Matthew Perry already has been cast as the grown-up version of Efron, while Leslie Mann plays his wife.

Trachtenberg is playing Efron/Perry's daughter, who doesn't know that the boy she is crushing on is her father. Hardin is the principal at the school.

Production begins this month.

Trachtenberg, repped by CAA and Framework, next appears alongside Topher Grace in Universal/Imagine's "Kids in America."

Hardin is best known for her work as Jan, Steve Carell's put-upon lover, in NBC's "The Office." She appears in the Katherine Heigl rom-com "27 Dresses." She is repped by the Kohner Agency.