Many filmmakers feel the only way to show a character grow up during a movie is to actually shoot the film over a period long enough to allow the actor to age naturally, but this is generally not feasible because Hollywood demands sacrificial offerings movies on a yearly, if not quarterly, basis.
A new film called Boyhood is about to change those rules, because this feature film depicts a child star actually growing up during production, a feat that took twelve years of filming to accomplish.
Director Richard Linklater wanted to make a film that showed "a parent-child relationship that follows a boy from the 1st through the 12th grade and ends with him going off to college", but to do that he had to film scenes once a year for twelve years, changing the script as needed to keep up with how the boy changed in real life over the years.
It's a bold experiment in humanistic filmmaking, one which movie studios are unlikely to repeat anytime soon.
-Via 22 Words