Not even Joseph Conrad had the courage to venture into that darkest of hearts: middle school.

Bo Burnham's "Eighth Grade," however, plunges us into the day-to-day experience of a 13-year-old girl, Kayla Day (Elsie Fisher) with just as much intensity as a journey down the Congo. Every sling and arrow, in the mall food court or on Snapchat, is felt acutely. Whenever Kayla's crush, the (to her eyes) smoldering Aiden (Luke Prael), steps in the room, the world turns slow-motion and the music thunders. End-of-the-year superlatives? The horror.

Such harrowing moments have long been stretched for their comedy ("Middle School: The Worst Years of My Life") or their torture ("Welcome to the Dollhouse"), but rarely have they been rendered with such precision and empathy. Burnham's intimate, impressive directorial debut is armed not just with an understanding for the awkwardness of youth but with an anger at what social media and cell phones are doing to it.

The 27-year-old former YouTube sensation turned stand-up comedian turned feature filmmaker is an unlikely guide for such a crucible of adolescence. Burnham's comedy, while evolving, has typically been theatrically, even combatively brash. His rise was propelled by the technology he's now turning on.

Like Burnham did as a teenager, Kayla hosts a YouTube show, only nobody watches her earnest life advice. "The hard part about being yourself is that it's not easy," she says into her bedroom camera before reminding viewers to hit "like" and signing off with a forced trademark: "Gucci!" Sweet, shy and acne-covered, Kayla lacks both an audience and friends. Only one of those matters.

Kayla tries, unconvincingly, to project a confident version of herself online while struggling through lonely days at school. On YouTube, she insists that she just chooses not to talk a lot. At school, she's named "quietest." Her loving single dad (an adorable Josh Hamilton) is seemingly the only one in her corner, and she mostly just sighs at him or tunes him out his very dad-ish entreaties with earbuds.

From the start, we feel the unreasonable pressure put on Kayla by blissful Instagram accounts and savvier Twitter feeds. She spends much of her days and nights anxiously scrolling down screens, fueling her insecurity (certainly not an affliction reserved only for teens). In one scene, Kayla wakes up, does her makeup from a YouTube tutorial, and then crawls back into bed to take a Snapchat selfie. That the Internet is damaging Kayla isn't hard to get; when her iPhone screen cracks, she pricks her finger on it.

But she is gloriously plucky. The Post-its on her mirror read "Go get 'em!" and "Be sexy!" When an already cringe-inducing birthday party sets up karaoke, we start covering our eyes for the all certain embarrassment to come. But she goes for it. Burnham keeps the camera focused on Kayla and her personal triumph, not the reaction of the teen onlookers. Sorry, Rock. Kayla is the summer's most awe-inspiring hero.

Another movie might lead inevitably toward scenes of bullying. While there are dramatic confrontations, "Eighth Grade" is subtler and its focus more inward. There's the cool girl Kennedy (Catherine Oliviere) and an intimidating group of older kids, some nice, some not. But what Kayla most needs is to simply recognize, as her dad pleads, that she's "so cool."

We know that Kayla is going to be OK, but "Eighth Grade" hangs on whether she's going to realize it herself soon enough. Fisher, who voiced Agnes in the "Despicable Me" movies, is extraordinary. "Eighth Grade" is a revelation of both a remarkably natural young performer and a clever, sensitive young filmmaker. As if with battle scars from his youthful days consumed by social media, Burnham has returned from the Millennial trenches like a war reporter.

Largely on the outskirts throughout the film, adults are clueless to what's going on, making only comical gestures at bridging the generation gap. A sex-ed video host promises a lesson is "gonna be lit." The principal tries to dab. When Kennedy's mom tells Kayla that Kennedy will send her a birthday party invitation on Facebook, Kennedy seethes: "Mom, nobody uses Facebook anymore."

That parents should see "Eighth Grade" is a given, just as it that middle-school kids should, too. But would Kayla see "Eighth Grade"? She has her nose so firmly in her laptop and phone that I fear not. "Eighth Grade" is one more good reason to log off.

"Eighth Grade," an A24 release, is rated R by the Motion Picture Association of America for "language and some sexual material." Running time: 94 minutes. Three and a half stars out of four.

___

Follow Jake Coyle on Twitter at: http://twitter.com/jakecoyleAP