Slain NYPD rookie Officer Jason Rivera told high school freshmen “to put in the work” to make it in life, he said in an inspirational video filmed when he graduated.

In a heartfelt video message when he graduated Washington Heights Expeditionary Learning School in 2017, Rivera urged younger students to work hard or they would make it “nowhere” in life.

“High school is high school. Like, you know what? We don’t like it but we still have to do it,” he says in the clip, which was also posted to Instagram by his alma mater. “And I want y’all to do it. Because when I was a freshman, I didn’t have no one to motivate me. I want to motivate ya.

“Ya gotta put in the work. Ya gotta put in 100 percent effort. And ya know what? If it takes some time after school, ya know, so be it, because you gotta do it. If you don’t do it you’re not gonna make it nowhere in life.”

As a ninth grader, Rivera was part of a student team that raised $5,000 for the Safe Passage Project, a nonprofit which provides lawyers to immigrant and refugee children in New York City and Long Island, his school said, posting a picture of the teen grinning ear-to-ear next to an oversized check.

Rivera demonstrated that he had a determined spirit and a way with words in his college application “personal statement,” former teacher Jared Fox told The Post.

“I sometimes sit in my room alone and just think to myself that life is not easy,” Rivera wrote. “Sometimes you are thrown a ball, and you have to learn how to dodge that ball. You can either stay hurt from the ball thrown at you, or you can work hard and heal again.”

Rivera went on to attend Borough of Manhattan Community College and Lehman College, before he joined the NYPD in November 2020. He said he was inspired to go into police work to improve relations between community members and officers in his neighborhood.

In an earnest “Why I Became a Police Officer” letter obtained by The Post, Rivera said he was once “bothered” when officers stopped and frisked his brother, but grew to realize he wanted to be an agent for positive change in the NYPD, and help people from all walks of life.

“I know that something as small as helping a tourist with directions, or helping a couple resolve an issue, will put a smile on someone’s face,” he wrote.

Rivera, 22, was fatally shot Friday evening responding to a 911 call from a woman who was in a dispute with her son in a Harlem apartment. His partner, Wilbert Mora, remained in critical condition Saturday.