Brainstorm (National Theatre)

The stage is a tip – covered in duvets and dirty laundry and all the other detritus of teenage bedrooms. In amongst the mess, ten teens stand with their heads in their smartphones and their fingers on fire. It’s a familiar sight: distant, unengaged and absorbed, communicating only in grunts and mumbles.

On a screen above though, spooling like a data stream, is a live feed of their Whatsapp group: words whirring upwards, a million messages a minute. All these acronyms and emojis, another language entirely. Ping. Ping. Ping. Ping. It’s a marvel to watch.

Devised with directors Ned Glasier and Emily Lim, Brainstorm lets us see into the heads of these teens – in more ways than one. We see both what they’re thinking and how their brains think.

The group are all members of the Islington Community Theatre, aged between 14 and 18, and Brainstorm lets them vent their frustrations, share their secrets and voice all the noise in their heads. We see volatile social lives and private vulnerabilities, swirling hopes and dreams, an influx of new information. "My brain is like my bedroom," says one. "It’s a mess."

The repeated frustration is the pressure to grow up and act like adults. It’s a sharp reminder that teenagers aren’t "just crap adults" and, threaded throughout, like the ‘sciencey bit’ in a shampoo advert, are facts about the teenage brain. It’s developing and it’s different.

Theirs have more synaptic connections, forging new neural pathways as they’re flooded with fresh ideas, making sense of the world. All that reckless behaviour, that’s the result of a hyperactive limbic system, the part of the brain that rewards risk, and an underdeveloped pre-frontal cortex, the part that keeps us under control. "My brain isn’t finished yet," another one says. "I’m becoming who I am."

It’s not far off the phrase that stuck out of Ontroerend Goed’s trilogy for teenagers: "Let me be." Brainstorm never quite finds the same soaring theatricality: it never lets its tyro cast off the leash and, while they mock their adult audience – there’s a cracking dad dancing sequence – it’s reluctant to really confront us. At some level, the science explains away all that natural teenage majesty.

They should challenge us because they do and they will. This is the next generation and, in time, they’ll reshape society for themselves. As they stare down at their phones, it’s like they’re downloading the whole world, ready to give it an upgrade. The make-up of their brains allow them to spot fresh possibilities and then allow them to chance it. Mark Zuckerberg was 19 when he created Facebook. Malala won the Nobel Peace Prize at 17. Anyone over 25 will feel the loss of their limbic system keenly.

Watching it, from an adult perspective, is both fondly nostalgic and sharply contemporary. It’s impossible not to whizz back through your own teenage years – rebellions, first snogs, park benches and all – and you swear to shift the way you treat today’s teens, whether as a parent or not. More importantly, it gives a voice to a portion of society all to often overlooked. Teenage kicks, indeed.

Brainstorm is at the National Theatre until 25th July.