Set in a sleepaway stage-training program for shy kids and incorrigible natural hams, where attendees get intensive instruction from Broadway burnouts, “Theater Camp” is that rare parody that has viewers laughing from the opening scene till the credits roll. I’m talking about the 18-minute short film that Noah Galvin, Molly Gordon, Nick Lieberman and Ben Platt uploaded to YouTube a month or so into the pandemic, earning a cult following among musical theater geeks and those who survived comparable drama camps in upstate New York. The feature version is more of the same, minus the laughs.

Truth be told, this new “Theater Camp” probably contains just as many laughs, except that now, nearly all of them are packed into the final half-hour of a gets-old-fast feature in which co-directors Gordon and Lieberman hammer the same joke ad nauseam. The driving concept behind “Theater Camp” — which sold to Searchlight for high seven figures at the Sundance Film Festival — is that it’s funny to watch a bunch of kids subjected to tough-love auditions and egregiously inappropriate acting exercises by unqualified adults. A pint-sized aspiring agent (Alan Kim, “Minari”) works the phones, hyping his classmates. Another boy (Donovan Colan) struggles with coming out — as straight — to his two dads.

Way back in 2008 (when quirky indies still stood a fighting chance at the box office), Focus Features threw down a whopping $10 million for “Hamlet 2,” a scripted film that starred Steve Coogan as a washed-up actor turned overambitious high school drama teacher who writes a not-quite-Shakespeare-caliber sequel for his students to perform. Hilarity ensued. Flash forward 15 years, and that concept feels quaint (“Hamlet 2” wasn’t even all that original then, following on the heels of “School of Rock” and “Razzle Dazzle”). These days, 18 minutes is already just about the maximum such a concept can sustain.

From the opening scene, which has Adirond Acts camp founder Joan Rubinsky (Amy Sedaris) suffering a strobe-induced seizure at a junior-high production of “Bye Bye Birdie,” “Theater Camp” seems to be trying too hard. Sedaris may be a comedic legend, but she disappears from the film far too soon. “After one day of filming, the subject of our documentary was now in a coma,” an intertitle explains. Yes, “our documentary.” Here we are in the year 2023, and people are still making mock docs. It’s easy to understand why, since the shakily handheld, haphazardly edited format helps to disguise a thin script and lean budget.

For that to work, it helps to have a cast of Christopher Guest-level improv talents, as opposed to a mix of precocious young thespians and adult theater-camp alums tossing out absurdist in-jokes about character motivations, professional frustrations and the perils of being nonunion. The core ensemble features Platt and Gordon as co-dependent besties Amos and Rebecca-Diane, who met at a failed Juilliard audition and have been amateur creative collaborators ever since; Jimmy Tatro as Joan’s son Troy, a tone-deaf social-media jock woefully ill-prepared for running the camp in her absence; and Galvin as Glenn, an undervalued jack-of-all-trades just waiting for his time to shine.

The cast may be largely comprised of kids, but the movie doesn’t feel like it was made for their demographic. Flamboyant gay costume designer Gigi (Owen Thiele) sounds like he’s been watching too much “RuPaul’s Drag Race.” Overly demanding dance instructor Clive (Nathan Lee Graham) tells the kids, “You need to know that only 3% of people make it. The rest of them end up in a mental facility or on a go-go box in Hell’s Kitchen.” The actors aren’t unappealing per se (post “Dear Evan Hansen,” Platt’s neuroses are kinda the point of his character), but they’re stuck in screechy self-parody mode, as editor Jon Philpot’s quick-cutting style and James McAlister’s enervating score amplify the sense of creative disorder.

While Sedaris’ character sits in a coma, Troy is tasked with finding a way to raise enough money to keep the bank from repossessing Adirond Acts — or worse, letting ritzy rival Camp Lakeside (represented by Patti Harrison) buy out the property. Troy AirBnb’s one of the cabins to raise some cash and hires out the kids to cater a local Rotary Club dinner — which the naive group approach as an immersive theater experience. That’s as close to landing a chuckle as the movie comes in its first hour (well, that and the moment “America’s Got Talent” discovery Luke Islam finishes his audition). Mostly, audiences are stuck watching everybody trying to be funny: testing out one-liners, singing off-key, panhandling for laughs. Running jokes trip over their own shoelaces.

And then something amazing happens. All along, we’ve been told that Amos and Rebecca-Diane have been writing an original musical, “Still, Joan,” about their beloved mentor, who sits in a coma (the title is a wink at the 2014 movie that won Julianne Moore an Oscar). Rebecca-Diane’s been distracted for most of the movie, and the night before the big show, it’s revealed that she’s booked a gig on a cruise line — which any aspiring Broadway actor will recognize as the last resort, only slightly less pathetic than teaching youth theater. Anyway, after weeks of chaos, the moment of truth finally comes … and “Still, Joan” is kinda genius.

I don’t want to oversell the film’s big finale, but the creative team have actually come up with a suite of catchy, clever original songs about the fictional Joan Rubinsky, a self-made immigrant who abandoned a successful Wall Street career in order to dedicate her life to inspiring kids to embrace their dramatic potential. And it works. All of a sudden, after feeling like a runaway tornado, “Theater Camp” snaps into place. Anyone who’s ever participated in a pageant or play as a kid (and who hasn’t?) will recognize that feeling, as the whole troupe rises to the occasion and produces something they can be proud of. Was it worth all the headaches it took to get here? Maybe not, but at least it sends folks home with a smile on their faces.