'Buffy' Sis Turns '17'

Michelle Trachtenberg will join Zac Efron in the high concept comedy "17."

Also signing on for the New Line comedy is Melora Hardin ("The Office"), while previously announced cast members included Leslie Mann and Matthew Perry.

Production on "17" begins later this month.

Scripted by Jason Filardi, the Burr Steers-directed "17" focuses on a middle-aged father (Perry), who mystically, magically, inexplicably wakes up one morning to discover he's 17 again (and played by Efron). He has to go through high school again, which is bound to confuse his wife (Mann) and kids.

According to The Hollywood Reporter, Trachtenberg plays the main character's daughter/new school chum, which makes things extra awkward when she gets a crush on her dad (like "Back to the Future," only a slightly different movie). Hardin will play a high school principal.

Star of "Harriet the Spy" and "Ice Princess," Trachtenberg is still probably best known as magical sis Dawn from "Buffy the Vampire Slayer." She's most recently been seen in "Black Christmas" and "Beautiful Ohio," with "Kids in America" set for release next year.