Marta Cunningham's documentary "Valentine Road" may not be what you're expecting when you read the words "school shooting." The extraordinary thing about the film — which profiles the aftermath of a 2008 incident in which an angry 14-year-old middle schooler brought a gun to school and shot a classmate in the back of the head — is that many people may not have heard of its real-life subjects at all.

Cunningham herself lives in California, the same state where Brandon McInerney shot Lawrence King on Feb. 12, 2008, but only learned about the shooting after reading an article in Newsweek magazine. "It just seemed to be a blip on the radar," Cunningham said. "That was shocking to me."

What's known about the cause of the incident is simple and horrifying. "Larry had a crush on Brandon," Cunningham said. "Larry went up to Brandon on the basketball court and asked him to be his valentine. Within two days he was dead." As Cunningham put it, "We've all had crushes, we've all been 14. The finality of his death was horrific."

Driven to understand the incident, Cunningham attended every court proceeding that grew out of it, and began to meet and talk with students and families affected by the shooting. Four years later, "Valentine Road" will premiere in the U.S. Documentary Competition at the 2013 Sundance Film Festival.

Producer Sasha Alpert, who worked on "Valentine Road" with Cunningham, said that the proximity of Oxnard, Calif., where the shooting occurred, to her own home in Los Angeles, shook her up. "I have children who go to school in Los Angeles," she said. Almost equally disturbing, Alpert said, was the occurrence of an ugly hate crime so near to a large, urban population center: "We think of ourselves as being very broad-minded and accepting."

Though the incidents are different, the December shooting at Sandy Hook Elementary School in Connecticut has added a layer of urgency to much of what "Valentine Road" has to say. In making the film, Cunningham said, she talked to many parents who told her how difficult it is to help children process such a tragedy. "One of them said specifically to me, 'I want to talk to you. I want people to know: What do you say to your child when this happens?' "

And there are disturbing parallels to the Sandy Hook shooting. "Brandon was living in a home where there was an arsenal of weapons," Alpert said. "If you're choosing to arm your communities, as we have chosen as a nation, you need to have some kind of education."

That includes, Cunningham stressed, education about how to deal with people who are different than you may be. "We need to be careful what we say and how we act," Cunningham said. "Children are listening to what we say."