In his Berlinale competition title “My Brother’s Name Is Robert and He Is an Idiot,” Philip Groening examines the magical time of youth, being on the cusp of adulthood and impending separation for a brother and sister.

The acclaimed German filmmaker behind the hit 2005 documentary “Into Great Silence” and 2013’s “The Policeman’s Wife” says his latest feature is “about time, about philosophy, about adolescence, about growing up.”

Spanning 48 hours over a summer weekend in the country, the film follows the twin 18-year-old siblings Robert (Josef Mattes) and Elena (Julia Zange) as they spend their last days together studying philosophy at a gas station near a lake, preparing to part ways for the first time.

It’s a tale that came to Groening 18 years ago and one he intended to make with actress Sabine Timoteo, who starred in his 2000 road movie “L’Amour” (“Love, Money, Love”).

While Groening was unable to finance it at the time, he and Timoteo went on to develop the story together over the years, and Timoteo is credited as a co-writer on the film. “Of course, actors have a fantastic sense for dialogue and situations and for truth of scenes,” he pointed out.

The filmmaker finds youth a compelling theme. “In adolescence the elements of the personality you had as a child are sort of scattered, and suddenly they fall back into place in different order. And that’s fascinating because it’s really sort of the moment when your new personality will come together and will stay with you.

“Adolescence is a moment of such high vulnerability and also of such transparency. Everything becomes visible, which is later on very often in adult life kind of covered up.”

Groening found the ideal actors for his film, but it wasn’t easy. For the director, casting is less about finding the best actor for a part and more about finding the “best combination of actors for the film.”

“It’s kind of like choosing colors for the film. There was another couple of actors that might have been interesting, but it would have completely changed the tone and the emotional colors of the film. These are just perfect for me.”

While Mattes is an established young actor, Zange, a writer, had never acted before.

Groening enjoys working with people who are at the beginning of their acting careers, or who have not even acted yet. “There’s a sense of truthfulness when actors are starting to explore their trade. Sometimes it gets covered up later on. It’s a naturalness. The presence they have on the screen can be very, very strong.”

In addition to his own filmmaking, Groening also teaches and currently serves as a professor at the Internationale Filmschule in Cologne. He has also taught at the Filmakademie Baden-Württemberg and at CalArts in Southern California.

Teaching plays a significant role for the filmmaker. “Teaching means I have to understand what I’m doing as a director in order to talk with young directors about how to approach their work.”

“Of course it’s great fun to help students and young directors to develop their own personalities as artists, as filmmakers. And you also learn a lot from your students.”

One of his past students, Kolja Malik, is in this year’s Perspektive Deutsches Kino sidebar with “Storkow Kalifornia,” a film he made in one of Gröning’s courses at the Filmakademie.

“It’s a good example of how you can make a film with no money at all, a lot of energy and by just wanting to do it. And it’s a good film.”