Interview: Chris Weitz, director

CHRIS Weitz insists his moving new film, A Better Life, is not "overtly political", but it makes no attempt to mitigate the barbarity of the US's current immigration laws. There are 11.2 million illegal immigrants in the US, and the people who skim leaves out of pools or look after children often live a step away from deportation. Without papers to get a driving licence or healthcare, it's a precarious existence.

At the heart of the story is a father, Carlos (Demin Bechir), and his teenage son, Luis (Jos Julin). Carlos is an illegal immigrant but Luis, born in Los Angeles, is a US citizen. Carlos tries to make ends meet as a gardener, while Luis is at school, struggling to work out where he fits in. They are united only by the dilapidated house they share, and barely know each other.

What keeps Weitz's film together is the performances of Bechir, a huge star in Mexico, and Julin in his first role. Bechir exudes a quiet, stoic dignity in the face of a life spiralling out of control, while Julin captures the frustration of a teenager who can't respect his father because nothing around him - at school, or on TV, or in the gangs that control his neighbourhood - tells him he should.

"Demian is from acting royalty in Mexico," Weitz says. "He really understands what it is to create a role and give a performance. He really did help Jos to understand how to do that. We established a past for Carlos that was quite radically different from the character you see. He was a fighter and a drinker, he probably had beaten his wife at some point. There is a notion of remorse that comes into it. He's a man who has learned something."

For Weitz, Julin was a real find. "He's a genuine cinephile," Weitz says. "He's homeschooled so he has a lot of time on his hands and he will watch a directors' entire body of work over the course of a week or a weekend and then call me and say, 'I've watched all of Oliver Stone's films, what do you think?' And I have to say, well actually, I haven't seen all of them." He laughs. "He was a bit of a miracle for the movie."

A Better Life has been gestating for 20 years. A tricky subject in the US, it's not an easy sell. It started with TV producer Paul Junger Witt (The Golden Girls) who heard a story about a gardener that reminded him of the 1948 Italian classic Bicycle Thieves, in which a father and son go in search of a stolen bike in Rome. For Weitz, it was important to make the film as authentic as possible, but he's given it a universal resonance.

For a director best known for helming an instalment of the Twilight juggernaut, and American Pie, Weitz is not what you might expect.He's quietly spoken and cerebral, and with A Better Life it's clear he's found a project that is meaningful to him. Not least because there is a personal connection. His grandmother, 100-year-old Lupita Tovar, is a Mexican-born actress who emigrated to the US in the 1930s and his wife, Mercedes Martinez, is Cuban-Mexican. He took Spanish lessons before filming to keep an authentic atmosphere on the set.

But Weitz hasn't made a conventional, rough-around-the-edges, indie flick. "The received wisdom is that it would all be done on digital and it would look very gritty," he says, "But I really wanted it to be a beautiful film visually, which would allow us to sidestep a few clichs."

Weitz grew up in New York, but has lived in LA for nearly 20 years. It's a city he says is impossible to know in its entirety. "People bypass each other," he says. "They take the freeways past neighbourhoods they'd rather not know about because they've been told that they are dangerous with the result that people are suspicious of and frightened of one another."The film was shot in 69 locations - something Weitz now describes as "ridiculous" - so it shows a side of LA few people have seen. Weitz credits his location team who liaised with communities - often in areas of the city that had never been filmed before, such as the housing estate Romona Gardens where Luis and his friends hang out - and Father Gregory Boyle, a Jesuit priest who runs Homeboy Industries, a gang intervention project which uses the tagline "nothing stops a bullet like a job". Father Boyle helped Weitz get gang members and ex-members on board. "Having his assistance, his tremendous moral force behind us, was just brilliant," Weitz says. The script was checked by gang members to ensure the language, expletive and jargon-laden Spanish mixed with English, was right. Weitz also reshot a scene when Boyle queried its accuracy. But having ex-gang members involved did more than inform the details of the film.

"What you really get is a sense of profound sadness from the guys who've been in it for a long time," Weitz says. "There was a guy on the set who really felt like he wasn't going to be around for much longer. He'd got out of jail because he turned witness against some other guys who'd asked him to kill someone."

Weitz says people have told him they've had their mind changed in the two hours of watching the film. He's modest as he talks about it, but it's clear he's also ambitious for what the film might achieve: "There may be some people who change their attitudes. I've never wanted to preach to the choir. The classic example for me is that when I saw The Killing Fields. I'd never heard of Cambodia, let alone known that genocide had taken place, and yet everybody knows about Cambodia now. That movie changed the world. Ours is smaller and more modest but it could change people's minds about things."

• A Better Life is out now.