Get ready for the most amazing experience you'll ever have in a cinema. Seriously. Shot over 12 years, Richard Linklater's time-lapse epic Boyhood is all that its title suggests. Every year since 2002, the Austin-based auteur has gathered together the same cast – including Ethan Hawke and Patricia Arquette – to shoot scenes for the film. The results make BBC's ground-breaking Up series – which has periodically dropped in on 14 different Britons since 1963 – seem rather half-hearted. This is as close to the human experience as film-making can get.

“Ultimately, it’s a pretty big collaboration with everyone’s sense of reality,” says the 53-year-old Linklater. “I see myself in the kids. I see my own kids. I see myself in the parents. To me, it was always a film about bumbling through parenthood. It’s a portrait of trying to figure that out. And I think Ethan and Patricia see the same things. So we were all feeling it from all these different directions.”

It's a multi-faceted narrative masked by a singular trajectory. Boyhood comprises a series of episodes in the life of Mason, starting when he is six and continuing until he enters college at 18. Throughout, Mason is played by Ellar Coltrane, a local Austin actor. Despite his youth and inexperience at the start of the project – Ellar had only appeared in a few commercials before Linklater cast him in Boyhood's central role – the director describes the star as "the rock" of the hugely ambitious project.

“I always thought that one time I would call Ellar and he’d say: ‘You know, I don’t really want to do this anymore’. But that never happened. He was always ready to go. It was kind of amazing. Patricia and Ethan were professionals. They served. They worked hard and came in and did everything possible. But they weren’t local. I couldn’t just call them up come see them and talk about what’s going on. By the end, Ellar felt like my nephew or something. He was part of the family.”

That sense of family was compounded by the presence of Lorelei Linklater, Richard's daughter, who plays Mason's older sister. As with Ellar, Lorelei was seven at the start of production and is 19 by the time the credits roll.

“Once it was clear that the older sister was within her age range, there was no way she was going to allow me to cast anyone else,” laughs the film-maker. “I never even looked at anyone else. She just told me: ‘Oh well, I’m playing that role.’ And I thought: ‘Well good. Because I know where you’re going to be every year.”

The Slacker-Philosopher But what was about Ellar that sealed the deal? How did he know that the six-year-old he cast in 2002 would grow up to be, well, a typical slacker-philosopher Linklater character?

“Looking back, meeting him was the moment that made the film,” says the Oscar- nominated writer-director. “He was the interesting, arty, mysterious kid, you know? Kind of poetic in his own way. A lot of charisma. Other kids were more quote-unquote ‘straight’. They might have been the class president or the really popular guy at school. In a way, I was the other kids. I was the kid who played sports and did all that. But I think Ellar was almost like the more interesting part of myself. He’s the part I’d rather make a film about.”

He laughs. “Not this boring kid like I was.”

For anyone born during the 1990s – or for anyone who knows anyone born in the 1990s – Boyhood provides a series of poignant temporal markers in the form of successive gaming systems. Although music from Coldplay, Arcade Fire and Lady Gaga plays and there's a midnight Harry Potter queue at the book store, the technological cues – Wii eclipses Xbox eclipses Nintendo DS – are somehow the most loaded.

“I think that’s right,” says Linklater. “We were making a period film in the present tense. It’s not often you get that chance. It used to be that cars and fashion and music would tell you when you were. But those things aren’t so reliable anymore. It was a fun collaboration that way. I didn’t want to rub that stuff in too much. But you can’t go wrong using technology as a marker. And games are such a big part of a young boy’s life. I had to keep thinking, ‘how is this going to look and feel 10 or 12 or 18 years from now?’ And regardless, if this thing is still around, then this is the first year they had it.”

It's not just the games. Throughout Boyhood, Linklater incorporated Ellar's various interests as they shifted between making arrow rock heads to graffiti to photography. When Mason rants onscreen about removing his profile from Facebook and resisting the pressure of living life through a screen, it's because Ellar said it first.

“The single most interesting thing in the entire process was watching Ellar become a more active collaborator,” says Linklater. “You’re dealing with a kid who can just about read the scenes – and he’s very attentive and trying. By the end, I was working with him the same way I would Patricia or Ethan any other actor. What’s going on in your life? How do you feel about this? I can say that’s not really Ellar at the beginning. He’s playing a part. He’s a very different kid. But at the end when he’s wondering about sex and life and love – to some degree, that is him. At that moment. And I told him this early on. That at some point this is going to blur into you.”

Something So Personal He didn't screen any of the film for Lorelei or Ellar until Boyhood was complete. But he did allow his adult cast a few sneak peeks. Why?

“You know, it never really came up. The kids never really asked. But my instinct was not to show them anything. As a kid, I remember being shocked when I saw or heard representations of myself. ‘That’s not what I look like. That’s not what I sound like.’ I still think like that. I’ve never got used to it.”

And when they did?

“I gave each of them a DVD and told them to watch it alone. It’s tough enough to watch something so personal. Ellar watched it alone several times. I told him build up his own relationship with this movie. It’s a heavy thing and I don’t think many actors have ever faced this unique thing of seeing themselves grow up on screen. Ellar’s a little more chill with it, the way I think some guys just are. Lorelei, like a lot of young women, with the pressure that society puts on young women, thinks she looks hideous or fat here and there. She thinks the most horrible things. She doesn’t give herself a break, you know?”

Perhaps the most surprising and strangely powerful aspect of Boyhood is the understated nature of the drama. The tableaux we do see can record major events, but often after the fact. We don't see Mason break up with his first steady girlfriend, but we do see them wondering what do to with their prom tickets afterwards. We're not entirely sure when Ethan Hawke's Mason Sr transforms from a deadbeat, weed-smoking dad into a straight-laced realtor with a Christian wife, but we do see the new baby and meet the good ol' in-laws. Indeed, one of the film's few properly dramatic moments happens when Mason's stepfather takes him for an unwanted haircut.

Linklater laughs loudly: “I love that that’s probably the most traumatic scene in the film. In real life, filming that scene was easy. We made Ellar keep his hair longer than usual. It was one of the only times we ever put any kind of restriction on him. It’s funny for me. He’s staring a hole through everybody, when really he was so happy to get his hair cut that day. It just proves what a good actor he was.”

As Ellar’s Mason is transforming, so does his mom, Olivia, as played by Patricia Arquette. A single parent who struggles with a series of disastrous relationships, she finally discovers herself in academia. Why did all her menfolk have to be such jerks?

“Ha. They never start that way. Let’s not forget they’re probably not as bad as they seem, because you’re seeing them through Mason’s point of view. I had a couple of stepfathers, and I think they weren’t probably as bad as I remember them. I just resented their presence. ‘You’re here in my life exerting some authority.’

“When you’re a kid, you’re so self-absorbed. Step-parents are like metaphor for life. Like school, they are foist upon you. Now I feel that they were probably bumbling through just like everybody else. It’s tough being a human.”

For long-time admirers of Linklater, Boyhood will immediately feel like his magnum opus. The indie auteur behind Dazed and Confused, School of Rock and Fast Food Nation has long deserved his reputation as the slacker poet laureate. But equally, Linklater has always been fascinated by the remembrance of things past, as exemplified by the Before Sunrise trilogy. What is it about Richard Linklater and the passage of time, I wonder?

“I do think a lot about cinema and storytelling. And I do think of time as the essence of cinema. A lot of my narrative strategies come from time. Plot is an artificial construct. Time is a more natural structure. It’s the way the human mind words. So for me, it’s a very obvious way to tell a story.”