For proof that the influence of a great teacher can last a lifetime, look no further than Sandra Mittelman, who retired in 2012 after teaching English at Russell Sage JHS in Forest Hills for 21 years.

Last month, Mittelman was surprised to receive an email inviting her to a film premiere at the Tribeca Film Festival — from a former student whose script was inspired by Mittelman’s curriculum.

“It’s so exciting,” said Mittelman outside the theater on Friday, April 18 after a joyous reunion with her student, Liska Ostojic. “As a teacher, you always wonder where your students have gone. This feels validating.”

Ostojic was in Mittelman’s 7^th-grade English class in 1995 when the class read “Lather and Nothing Else,” a short story by Colombian writer Hernando Téllez.

“It stayed with me for years,” says Ostojic of the story, which follows the inner monologue of a barber — who is also an undercover rebel working to overthrow his country’s military rulers — as he is shaving a customer who happens to be a military captain. “It’s not exaggerating to say the stories I read in Mrs. Mittelman’s class shaped my life and what I think of the world.”

As a film student at the American Film Institute in Los Angeles, Ostojic wrote a script inspired by the story. The resulting short film, “Contrapelo,” which was directed by Ostojic’s classmate Gareth Dunnet-Alcocer, was selected from more than 3,000 submissions to have its world premiere at the Tribeca Film Festival.

At a coffee shop before the film, Mittelman — accompanied by her daughter, Avigail Gordon — reminisced with Ostojic and several other students from the same class who also attended the premiere. The women laughed as they recalled assignments that had made a lasting impact.

“I remember you made us write an internal monologue from the perspective of the captain, and I still have it to this day!” said former student Aleksandra Zolley.

For Mittelman, it was a sweet epilogue to a long and fulfilling career.

“My background was in library, and I never wanted to teach,” she reflected. “But after a few years, it just felt so right.”

And her former students were gratified to learn that their affection for Mittelman was reciprocal.

“A class like yours,” Mittelman told them, “was heaven on earth.”