In the summer of 2018, as the midterms heated up and the Trump administration made a national flashpoint out of America’s southern border, over a thousand high school boys descended on the state capitol in Austin, Texas, with one mission: elect and run a state government.

The week-long simulation of representative democracy known as “Boys State”, designed to cultivate America’s next generation of political leaders (prior participants include Bill Clinton, Cory Booker and Dick Cheney), had made headlines the year prior for passing a resolution for Texas to secede from the Union. That debacle – a miniature of America’s rightwing, spectacle-hijacked political system – caught the attention of married film-makers Jesse Moss and Amanda McBaine, who joined the boys at the capitol, cameras in hand.

Their fly-on-the-wall film Boys State, the Sundance Grand Jury documentary prize winner began with the hope to explore “a space in which people of different political viewpoints were actually getting together and trying to talk to each other,” Moss told the Guardian. But by the end of the first hour of filming, the event was less model UN discourse and more testosterone-fueled chaos careening into cafeteria-style political campaigns. Some boys immediately jump at higher office, others gain notoriety through party-specific meme accounts; one group uses their time to propose a ban on cargo shorts.

“Suddenly they hand the program to the boys, for worse and for better,” said McBaine. “And for a moment, it’s Lord of the Flies.”

Boys State embeds in a half-dozen vantages within the simulation, created by the American Legion in 1935 to counter socialism’s Young Pioneer camps; over the course of 110 minutes, the film offers a fascinating and terrifying peek into the impulses and potential of the democratic model. McBaine and Moss follow participants of various political stripes as they gather signatures for their ballot, develop a party platform (the boys are arbitrarily split into two value-agnostic parties, the Federalists and the Nationalists) and campaign for program-wide office by the final day’s election.

McBaine and Moss spent three months before filming interviewing high school students at American Legion offices across the state, looking for a “cast” to follow – in vérité style, with the air of an elimination survival show – throughout the whirlwind week. In San Antonio, they met Ben Feinstein, a double-amputee and self-described “political junkie” who entered determined to run for governor, the program’s highest-ranking position, with a bootstraps mantra of “hard work will get you far, but you may need to work harder”.

In Houston, they discovered Steven Garza, a soft-spoken yet unwaveringly idealistic Latino student – son of a gas station worker, out of place among a largely white, conservative-skewing crowd – who arrives wearing a Beto O’Rourke T-shirt and emerges as the film’s star in his underdog run for governor.

Once filming, the crew followed Robert MacDougall, a roguish, swaggering charmer from Austin with second-nature magnetism of his peers, and René Otero, whose electrifying crowd command cements him as one of the leaders. A Chicago transplant and one of the program’s few black participants (“I’ve never seen so many white people in my life,” he remarks upon arrival) Otero’s unshakable confidence and cutting humor quickly win him favor – and a hostile, ugly impeachment backlash – as Nationalist party chairman opposite Feinstein, the Federalists’ win-at-all-costs chairman.

Boys State, as a film and exercise, doesn’t reflect the makeup of the nation – the Texas program is overwhelmingly white and there are, to noticeable effect, no women present (a separate program for girls also takes place) – yet the film nevertheless presents a consuming portal into both 2020 masculinity and the sliding scale of American political values. It can be heartwarming, when people such as Garza and Otero summon voters’ better natures, or when MacDougall adapts from obscuring his beliefs (he’s personally pro-choice but incorrectly assumes the majority of the crowd would be anti-abortion – “That’s politics,” he says, “sometimes you can’t win on the opinion in your heart”) to Garza’s heart-on-his-sleeve campaign.

And then there are the familiar strains – the ease with which demagoguery and showboating, particularly on the second amendment, drown out everything else; the power of one’s worst impulses, exacerbated by the performance of masculinity and concentrated in personal and racist attacks or gossip.

If anything, the barreling, unpredictable trajectory of the film, with all the buzzing energy you would expect from 1,100 17-year-old boys ping-ponging into self-governance, demonstrates that nothing in politics is inevitable or fixed; the compounding of individual choices, styles and levels of seriousness steer and alchemize the whole affair in ways breeding both hope and cynicism.

For the participants, now two years removed from the exercise, the week crystallized a variety of reflections on the fruits of political participation. The fish-in-conservative-water experience “is what every liberal needs”, Otero says halfway through the week, because it “forces you to think”. But by the end, Otero emerged disillusioned with the idea of running for political office, preferring instead the avenue of activism, education and non-profit work, though he noted to the Guardian that his experience as a party leader provided “hope” in that “there is an American public who understands what good leadership should look like”.

MacDougall, now 20 and a military cadet at West Point, reflected on his “that’s politics” stance of with more circumspection: “Way too often I think that is politics and I wish that it wasn’t,” he told the Guardian, and added that Garza’s campaign “showed me first-hand throughout the week that that does not have to be politics.”

“The fault of the simulation of Boys State is that it immediately pits the two parties not as separate entities coexisting, but two entities who hate each other,” Garza, now 19 and living in Houston, told the Guardian.

Still, he walked away from a Hollywood-level climactic election (no spoilers here) with “an even greater idealism than I had going into it, just knowing that you can build a coalition of people who don’t agree with each other, but want to support a certain candidate because they truly believe that that person wants to work with them”.

For Feinstein, who by the latter half of the week resorts to personal attacks on Garza’s gun rights activism and ludicrous but effective theater against Otero’s handling of town halls, rewatching the film prompted significant reflection on the tactics deployed to win. (“I think he’s a fantastic politician,” Otero says of Feinstein in the film, “but I don’t think ‘fantastic politician’ is a compliment, either”). “Had I known what was going on on the other side of the curtain,” seeing the fellow participants as potential friends rather than high-stakes enemies, “I might have acted differently,” Feinstein told the Guardian. Instead, he modeled what we see every day in the horserace mentality of American politics. “All the adults smear each other so of course when I’m 17 and I want to win, I’m like, ‘Let’s do it this way.’”

Watching Garza and Otero play to people’s better angels was, he added, “an important reminder that idealism can work and idealism should be the way it works.”

Ultimately, an exercise such as Boys State offers a “reminder that democracy isn’t a spectator sport”, said Moss. “It’s not something we can take for granted; its health and vitality depend on willingness to both understand it as a process and as something that we all need to individually invest in in different ways.”

“With the challenges that we see in representative democracy every day of our lives currently,” added McBaine, “I think that reminder was something that we felt we needed.”

• Boys State was originally scheduled for a theatrical release on 31 July but will now be available on Apple TV+ on 14 August and will premiere at Sundance London in the UK on 9 August