(CNN) Hard as it is to believe, Valentine's Day will mark the one-year anniversary of the mass shooting at Marjory Stoneman Douglas High School, which birthed a teen-led gun-control crusade. HBO marks that moment through a narrow window into it with "Song of Parkland," a half-hour documentary short that's equal parts uplifting and heartbreaking.

Spare and economical, the documentary essentially plays out between two events: the terrible killing of 17 teachers and students at the school, and a group of Marjory Stoneman theater students singing "Seasons of Love," from "Rent," in a huge emotional moment at last year's Tony Awards.

In between, producer-director Amy Schatz ("An Apology to Elephants") zeroes in on theater teacher Melody Herzfeld -- who offers a pointed reminder that these are teenagers, thrown into a horrific situation and the public spotlight -- seeking to recover a sense of normalcy.

"They're supposed to be kids first," Herzfeld says. "These kids that are making these speeches, and they're going up and being so strong, they can't even tie their shoes. They can't even remember to put deodorant on ... or remember their homework. But they're trying to, like, do something."

"Song of Parkland" captures with these youths have done, how they have forced a conversation about gun control, weathering the partisan attacks that come with entering the political arena as activists.

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