GLOUCESTER — As a kid, Sian Heder spent summers in Gloucester.
She’d go cliff jumping at the quarries, daring friends to scale 40 feet onto the rocks and dive into the water. Many years later, she had her actors do the same, in a teenage love scene featuring Emilia Jones and Ferdia Walsh-Peelo.
Gloucester is full of childhood memories for the 44-year-old Cambridge native, whose most recent film, “CODA,” is set in the coastal city. “CODA,” shot on Cape Ann, is Heder’s second feature to debut at the Sundance Film Festival, after “Tallulah” (2016). She has written for three seasons of the Netflix series “Orange Is the New Black” and is an executive producer for the Apple TV+ series “Little America.”
“CODA” starts streaming on Apple TV+ Aug. 13 and will be showing at the Coolidge Corner and Gloucester Cinema.
“CODA,” an acronym for Child of Deaf Adult, is a coming-of-age story about Ruby Rossi, the hearing daughter of a deaf fishing family. As Ruby navigates her senior year of high school — she joins a choir, has her first kiss, applies to college — she must also balance the responsibilities of her life as a CODA.
“Ruby is trapped between two worlds, the hearing world and the deaf world,” Heder said last month, over lunch at the Gloucester Beauport Hotel. “I was intrigued by the idea of this family, digging into the specificity of a culture that we don’t often get to see on screen.”
Statistics show that 90 percent of children born to deaf parents are hearing individuals. CODAs grow up signing as their first language and are often more culturally deaf than deaf people born to hearing parents. They carry deaf mannerisms, Heder said, like waving in someone’s face to get their attention or pounding on the table during a conversation.
“It’s a hard role to be in, because they do feel that it’s their culture. At the same time, they have all the privileges of a hearing person.”
In this adaptation of the 2014 French comedy-drama “La Famille Belier,” deaf characters are played by deaf actors. This wasn’t the case in the French film, which critics found problematic.
“I cannot imagine this story with hearing actors,” Heder said. “Imagine if this was some movie star who had to learn ASL for the role. It would be a nightmare.”
Hollywood doesn’t have the best record for deaf representation in film. Directors often cast hearing actors to play deaf characters. Even when deaf actors are cast in breakthrough roles, hearing characters speak the deaf person’s lines.
“It’s almost like the Oscars have incentivized non-disabled actors taking on disability,” Heder said. “If you look at movies like ‘Rain Man’  or ‘I Am Sam’  and the way that those actors were rewarded — we’re just not in a time anymore where that’s acceptable.”
The presumed challenges of working with deaf actors might deter filmmakers from casting them in films. How would communication work? What kinds of accommodations would have to be made on set?
“It’s a pretty lame excuse at this point,” Heder said. “You guys make movies. You blow up buildings, flip cars, and make Spider-Man swing. You can figure out how to put enough interpreters on your set.”
In preparation for “CODA,” Heder began taking ASL lessons and hired deaf collaborators. She made sure that the film was accessible to deaf audiences by using medium shots so as not to cut off actors’ signs, set design accurate to the deaf experience, and an ASL script true to Gloucester’s local dialect.
“In the same way that if you’re from Boston you want the Boston accents to sound right, there are regionalisms to sign language,” she said.
Casting deaf actors expanded the film’s creative potential. In a hilarious doctor’s office scene featuring Ruby (Jones), her father, Frank (Troy Kotsur), and her mother, Jackie (Oscar winner Marlee Matlin), Frank describes the symptoms of his genital thrush in vivid, somewhat chaotic detail. Heder recalled with stifled laughter that in one improvisation of the scene, Kotsur pulled out a lighter and started waving it under his signs — fire in the groin.
The deaf cast and crew even gave Heder a sign name, a unique identifier assigned to members of the deaf community.
“A sign name is something that can only be given to you by a deaf person, generally when they know you pretty well,” Heder said.
Much like a nickname, a sign name can be a letter. Matlin, for example, is known as MM, her initials in sign language. One of Heder’s ASL masters, Alexandria Wailes, assigned her the letter S, signed like the Superman symbol. But S for Sian never caught on.
Then one day during the shoot, her sign name became clear. The cast and crew crowded in the living room of the Rossis’ house. Rushing to complete a task, Heder stood up very quickly. That’s when she bumped heads with her assistant director.
“It was the hardest I’ve ever bonked heads with a person. We had cartoon birds flying over our heads,” she said.
“That was so loud even I heard that,” Kotsur told Heder.
From that point on, Heder’s sign name was Bonk. With both hands balled up into fists to show the letters for S, she clashed her hands into each other.
The team eventually settled on a new name for Heder before their Sundance debut: fluttering fingers, the sign for creativity, coming out of the eyes.
“I still feel more like I’m Bonk,” she said with a smile.
While producers worried that a film nearly half in ASL would lack commercial appeal, Apple paid over $25 million for the streaming rights to “CODA,” a record-breaking sale at Sundance, which topped the $17.5 million that Hulu paid last year for “Palm Springs.”
“It’s helpful that ‘Sound of Metal’ came out and ‘Crip Camp’ was nominated for an Oscar,” Heder said.
“Sound of Metal,” starring British-Pakistani actor Riz Ahmed, follows the story of a heavy metal drummer who loses his hearing. “Crip Camp: A Disability Revolution” tells the story of disabled teens at Camp Jened in 1971 and their journey to becoming disability rights activists. “Sound” was nominated for six Oscars, winning for best sound. “Crip Camp” was nominated for best feature documentary.
“All these movies released within the same time frame feel like a movement, as opposed to a singular breakthrough,” Heder said.
“CODA” continues to be an educational experience for the filmmaker, who intends to keep learning ASL. Now when she walks into a room, she is hyper-aware of its accessibility.
“I’m looking at the world through different eyes,” she said. “I hope this movie is a part of the movement.”