With his landmark trilogy—1995’s Before Sunrise, 2004’s Before Sunset and last year’s Before Midnight—independent filmmaking maverick Richard Linklater has spent 18 years tracking the lives of lovers Celine (Julie Delpy) and Jesse (Ethan Hawke) in an extended-storytelling experiment, checking in with the couple at nine-year intervals. But as risk-taking and successful as the Before films are, it’s his new picture, Boyhood, that expands and elevates the idea of following characters over a set period of time. Linklater’s epic look at growing-up’s mundane moments was shot in only 39 days—over the course of 12 years.

The Texan writer/director took a big gamble in 2002 when he rolled the dice on 6-year-old Ellar Coltrane, whose acting experience was limited to a couple of commercials. We first see his character, Mason Evans Jr., as a cute little moppet daydreaming in a grassy field beside his elementary school, squinting as he stares into the blue sky above. When Mason’s mom, Olivia (Patricia Arquette), arrives to pick him up, it’s a bit off-putting to see him look briefly into the camera, breaking the spell of naturalism that Linklater excels at creating. But things improve quickly.

Mason goes about everyday kid stuff—riding his bike, spraying graffiti, capturing early, erotic glimpses of breasts in lingerie catalogs. We’re introduced to his slightly older sister, Samantha (Lorelei Linklater, the director’s daughter), as Olivia reads her two children a bedtime story. But Linklater’s not interested only in an idyllic Norman Rockwell portrait of childhood. There’s pain, and much of it stems from alcohol abuse.

Olivia is tucking in Mason and Sam after their story when an unexpected visitor shows up in their home. Brandishing a beer, Ted (Steven Prince) is there to verbally abuse her for staying home with her children rather than partying with him that evening. During breakfast the next morning, Olivia informs Mason and Sam that they’ll be moving to another town. Thus begins another pattern in the film: flight from abusive relationships.

Moving into a new home in Houston, the brother and sister settle into new routines, with new friends and separate rooms. It’s all rather ordinary, almost stilted. But then Linklater produces an ace from his deck, introducing Mason Sr., played by Hawke. Stopping to visit his kids in his prized GTO, he takes them bowling, before telling them about the “big lie” of Iraq. “Who are you gonna vote for next fall?” he asks them. The three already know the response, which they recite together: “Anybody but Bush!”

This is one of many funny little signifiers that act as time capsules, buried throughout the film to clue us in on the year of the action. Some of these signposts are quite literal: By the end of W’s second term, Mason Sr. has the kids planting Obama signs on neighborhood lawns—and uprooting McCain posters. He has been away in Alaska. “I needed to take some time,” he tells them, adding, “Your mother’s a piece of work.” She’s also fiercely protective, sending her ex-husband packing when she finds him at the house upon her return home.

The narrative Linklater constructs is purely elliptical, and as we move through the years, it’s astonishing to see our protagonist, Mason Jr., becoming not only a better actor, but a more fully formed person. We witness his first pimples, his doughy early teens and his growth into a true individual; after many an abusive father figure has rolled through his life (his biological dad turns out to be the nicest and most grounded of the bunch), he develops an interest in photography, prompting one of his high-school teachers (Tom McTigue) to tell him that he won’t amount to anything. Mason knows better.

During this artsy phase, Mason meets a gorgeous girl, Sheena (Zoe Graham), who notes his earrings and his painted nails and comments, “You’re kind of weird, you know that?” Naturally, they begin dating. Heartbreak will probably follow, but while Linklater certainly shows us the hardships of life (more drunk husbands/stepfathers), he balances them with joys large and small.

His ever-changing facial hair charting the passing years, the elder Mason eventually remarries and begins a new family while growing closer with his first son. And while Olivia never finds her equal, she does discover the strength to survive on her own, putting herself through school and becoming a well-regarded professor—all while raising a couple of great kids. This is the finest work Arquette’s put on screen.

At Mason’s graduation party, during one of the rare moments alone with her first husband when she’s not sniping at him, Olivia observes, “Can you believe they’re both out of high school?”

“You did a great job with them,” Mason’s father admits. “Thanks,” she says. “I never thought I’d hear you say that.”

And neither did we. It’s just one of life’s little moments that makes this 2 hour, 46 minute film move so effortlessly fast.

Boyhood ***1/2
Starring Ellar Coltrane, Patricia Arquette, Lorelei Linklater, Marco Perella, Jamie Howard, Andrew Villarreal, Jenni Tooley, Richard Jones, Karen Jones, Brad Hawkins, Zoe Graham and Ethan Hawke. Written and directed by Richard Linklater. At Boston Common and Kendall Square.