ONCE A YEAR for 12 years, director Richard Linklater summoned a cast of actorsā€”including his own daughter Lorelei, who was nine when the project began, and Ellar Coltrane, who was sixā€”to film Boyhood, an utterly unique story of an utterly conventional American childhood.

Boyhood is set in the 21st century, so there are divorced parents and videogames; it's Texas, so there are guns. It unfolds over 12 years, from 2002 to the present, but there are no title cards to tell you that time is passingā€”instead, the years are ticked off with pop songs and Harry Potter book release parties, new haircuts and new best friends. The story is fictionalized, but the passage of time is real; the nearly three-hour result is an affecting, heartfelt masterpiece.

Olivia (Patricia Arquette) is a single mom raising two kids on her own after her flaky husband (Ethan Hawke) bailed on his young family. Though the film is primarily about the couple's young son, Mason (Coltrane), much of Mason's experience hinges on the lives and decisions of his parents, particularly in the early scenes. It's frustrating watching Olivia struggle to raise her kids, put herself through school, and find a satisfying relationship, while her musician ex-husband, freed from the burden of raising children at a young age, is allowed to enter adulthood on his own terms, spending years figuring out what he wants to do before easing effortlessly into a new family life.

There's no plot in Boyhood, per se, just the passage of timeā€”abrupt at first, jumping from year to year as young Mason hassles his big sister and tiptoes around a volatile stepdad, then more evenly as he enters adolescence and begins to show signs of the person he's going to become. It's nerve-wracking to watch a kid grow upā€”every time Mason gets into a car or roughhouses with his buddies, you worry for him; at the same time, you root for him to stand on his own two feet, to make the right decisions. Even as the kids in Boyhood steadily assert more and more independence, Linklater is painfully effective at conveying the sheer powerlessness of children, how they're stuck taking whatever the adults around them dish out.

In interviews, Linklater has explained that much of Mason's character came from the actor, Ellar Coltraneā€”and while that might be true, there's no denying that teenaged Mason is vintage Linklater. A rant about cellphones and Facebook could've come straight out of Waking Life; it's easy to imagine Mason drinking beer and bitching about Texas with Wiley Wiggins' character in Dazed and Confused.

Boyhood's emotional impact is cumulative: It's basically impossible not to be moved by the sight of children growing up onscreen. Life is moving. But individual scenes are powerful too, often in sidelong, surprising ways. The really pivotal moments in Mason's life happen offscreen: We don't see him graduate high school, but we get to hang out at the dorky party his mom throws for him afterward. We don't see him sleep with his first girlfriend, but we see him holding her on a rooftop in Austin, watching the sun come up. Boyhood could've easily felt like a highlights reel, an animated photo album of Significant Milestones. Instead, Linklater shows us the moments between the milestonesā€”and charts how the steady accumulation of experiences, good and bad, make us who we are.