“Boyhood” opens Friday at Sundance Cinemas. R, 2:45, four stars out of four. Mad Film Forum will host a “Madfilm Meetup” at Sundance at 8 p.m., Tuesday, with a pre-party featuring cocktails and music at 6 p.m. at the theater’s Rooftop Bar.

You could rate Richard Linklater’s new film “Boyhood” strictly on degree of difficulty, like an Olympic dive. Linklater has been making “Boyhood” since 2001, visiting the same group of actors each summer, adding more scenes as they grew older.  Ellar Coltrane was six when he was hired to play young Mason  , Lorelei Linklater (Richard’s daughter) was eight. The film is built around Ellar, and Linklater had no way of knowing what kind of actor he’d grow up to be. Embarking on such a project was a tremendous leap of faith for all parties.

Or you can just look at the finished movie. By that standard, “Boyhood” is one of the best of the year, a funny, moving and realistic look at growing up, looking backwards and looking forward. It’s like a naturalistic, conversation-heavy response to Terence Malick’s ethereal “Tree of Life,” which also dealt with epic themes of childhood and parenthood in Texas.

Mason starts off as an ordinary six-year-old kid living in Texas, playing with his friends, teased by his big sister. He lives with his burning-the-candle-at-both-ends mother (Patricia Arquette), his freespirited dad (Ethan Hawke) off in Alaska for the past 18 months.

And from there, life happens. Mom marries her college professor, who turns out to be an alcoholic jerk. Dad comes back to town, takes the kids out for bowling and baseball games, imparts some words of wisdom that he’d be wise to listen to himself. Year by year, Mason grows older, turning from a chubby-faced cutie to a snarky preteen, then to a philosophical teenage photography lover who starts wondering what it’s all about, anyway?

Linklater doesn’t use title cards or other signifiers to show the passage of time; the years just flow into each other, the way they do in our memories. We don’t see Mason graduate from high school, we see him at the party afterwards. Occasionally (and a little obtrusively at times), Linklater slips details into the film, pop culture references or scraps of conversation to signify what year we’re in. (“Wisconsin has the right idea. We should follow their example” tells us that it’s 2011.) Change happens to everyone in the family, whether they like it or not.

Linklater, always a ground-level filmmaker, finds the profound in the most ordinary and universal happenings, the moments between the moments, presented simply. A scene like Ellar painting over the hashmarks on a door jamb marking his and his sister’s height over the years packs such an emotional punch precisely because Linklater doesn’t dwell on it. Things just happen, and life pulls us ever onward.

The first time watching “Boyhood,” I found myself drawn to watching Mason grow up — Coltrane is such a genial, watchful presence. But the second time through, I found myself focusing on the parents’ aging. Arquette plays a woman who bounces from one jerky man to another before finally developing a hard-won sense of self, albeit a somewhat lonely one. And Hawke’s Mason, Sr. grows from being a self-consciously hip musician type into a devoted, even a little square, family man. There’s a scene of tentative reconciliation between Mason’s estranged parents late in the film, quick and offhand, that is almost unbearably poignant.

In a way, “Boyhood” is a thematic cousin to Linklater’s “Before” series, which has shown us how a couple changes and ages over 18 years. And there’s a bit of Linklater’s “Slacker” debut in the way Mason kind of floats through life — some of the philosophical speeches he makes at the end of the film sound a lot like a young Linklater at the start of “Slacker.”

But “Boyhood” may have more in common with Michael Apted’s “Up” documentaries, which visit the same group of kids every seven years of their lives, gradually getting older, the sum of the choices they made.

In a glorious finale, Mason goes to college and meets a girl who muses that maybe you don’t seize the moment, the moment seizes you. Linklater strings these ordinary moments together like Christmas lights to make an entrancing portrait of life.