Sometimes, one summer job can open the door to a lifelong career.

For Claudia Weill—groundbreaking director of the 1978 feature film Girlfriends—the opportunity came halfway through her undergraduate studies at Harvard University, where she was majoring in the venerable history and literature program.

“In 1967, which was the Summer of Love, I got a job working as a production assistant on a Paramount documentary in the Haight-Ashbury,” Ms. Weill recalled, sipping Earl Grey tea in her home overlooking Nashaquitsa Pond in Chilmark.

On Wednesday, July 24, the Film Center in Vineyard Haven will host a special screening of Girlfriends, followed by a discussion with Ms. Weill, ethicist Carol Gilligan and poet Honor Moore.

As the director’s assistant, Ms. Weill found herself doing just about every task, from the menial—“taking film to the lab, picking people up at the airport”—to the technical, holding boom microphones and other equipment as needed. She even stood in as an extra.

“Pretty soon, I found myself witnessing and learning about all aspects of making a film,” Ms. Weill said.

When it came time to edit the movie in New York, Ms. Weill’s course was clear.

“I left Harvard for a semester, which at the time was very outré,” she said. “People didn’t leave.”

Because she did, Ms. Weill learned editing first-hand with Carl Lerner, “one of the great film editors.” At the time his credits already included more than a dozen films, including 12 Angry Men, Requiem for a Heavyweight and Klute among them.

“He saw that I was really interested,” she said, and would give her a few reels to edit on her own and bring to him for critiques.

“It was a real stroke of luck for me,” Ms. Weill said. “As an apprentice editor, you couldn’t do anything creative.”

Working with Mr. Lerner taught Ms. Weill “how you tell a story through editing,” she said. “Editing is where the storytelling really happens in a documentary.”

Ms. Weill was thoroughly hooked by the time editing wrapped. Returning to Harvard, she remained in history and literature because the university didn’t offer a major in film. But Harvard did have the Visual and Environmental Studies program, housed in the Le Corbusier-designed Carpenter Center, and Ms. Weill made it her second home. After every filmmaking course she took, Ms. Weill would then sign on as a teaching assistant for the next class.

By the time she graduated, she had made two movies, both short documentaries focused on women’s work.

One, Metropole, paired footage of exotic dancers with backstage audio of what they were really thinking as they performed for men—laundry, errands and other everyday concerns. Already, Ms. Weill was exploring the inner lives of women in the era of second-wave feminism, roughly defined as a movement beginning in the 1960s that sought to advance beyond the original feminist goal of gaining the right to vote.

After graduation, she formed Cyclops Films with colleague Eli Noyes. The team made films for public television—Sesame Street’s Mad Painter series among them—and documentaries including This is the Home of Mrs. Levant Graham (1971).

With Joyce Chopra, Ms. Weill co-directed Joyce at 34, a documentary about Ms. Chopra’s pregancy at what then was considered a dangerously advanced age. That film opened more doors. After screening it for Shirley MacLaine, Ms. Weill found herself invited to film the first women’s delegation to China in 1973.

The resulting documentary, The Other Half of the Sky, was a 1975 Academy Award nominee. Ms. Weill was an established documentarian, but she was tiring of the job.

“I didn’t want to follow people with my camera, waiting for them to say what I thought they were going to say,” followed by months of editing to tease out a story, she said. “I thought, why not start with a script? Why not try a fiction film, which was a complete other animal,” Ms. Weill recalled.

Working with writer Vicki Polan, with grant funding so tight she could only film half the movie at a time, Ms. Weill made Girlfriends as an independent—no studio was producing films about real women’s lives.

“Most contemporary movies felt somewhat unreal to me,” she said. “They were not about me. I was never a character in any of the movies I went to.

“Most of them did not have strong female protagonists, or if they did they were very gorgeous, like Bonnie [Faye Dunaway in 1967’s Bonnie and Clyde].”

Girlfriends was—and remains—a standout achievement for the era, easily passing all three parts of the Bechdel Test nearly a decade before cartoonist Alison Bechdel formulated it in 1985:

1. The film has multiple female characters,
2. who talk to each other,
3. about something other than a man.

Lead actress Melanie Mayron, who would later star in the series Thirtysomething and more recently Jane the Virgin, plays an aspiring photographer in New York city whose poet roommate Anne, played by Anita Skinner, unexpectedly marries Bob Balaban and moves out.

The cast also includes a startlingly young and very far from famous Christopher Guest. “He was a kid,” Ms. Weill recalls, as well as Eli Wallach, who did not have to audition for his role.

“I met him at a party in the Hamptons,” she said. “I approached him and I said, ‘I’m making a really, really low budget feature. Would you consider playing a rabbi?’”

Girlfriends was a revelation not only in its storytelling, but for Ms. Weill’s directorial style. Strongly marked by her documentary-making experience, the film also is influenced by European directors of the era, such as Jean-Luc Godard, who were not afraid to let the camera linger on a subject or a scene where Hollywood might quickly cut to something new.

“The French new wave was very much on my mind,” she said. “I watched every film. They all flipped me out. That way of telling movies really interested me.”

The film took a long time to edit, and then a long time to sell, Ms. Weill said.

“The New York Film Festival turned it down. The New York film distributor for independent films turned it down.”

An invitation to the avant-garde Rotterdam Film Festival was the turning point. For the first time, Ms. Weill saw her film with an audience.

“People were laughing. I had forgotten it was a comedy!” she said. A distribution deal and a screening at Cannes followed, culminating in a sale to Warner Brothers.

Today’s critics credit Girlfriends with opening the way for more female-centered stories that have found wide audiences, television series Sex and the City and Girls (for which Ms. Weill has also directed episodes) among them.

The event on Wednesday at Martha’s Vineyard Film Center begins with a screening of Girlfriends at 7:30 p.m., followed by a question-and-answer session with Ms. Weill, Ms. Gilligan and Ms. Moore.

A friend of Ms. Weill’s since the 1970s, Ms. Moore—whose poetry stands in for Anne’s in the film—introduced the director to Ms. Gilligan last year.

“Honor felt the three of us would be a great [panel], in the context of second-wave feminism,” Ms. Weill said.

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