Annual media coverage of August’s exam results has traditionally conformed to an unwritten rule that all photos must show euphoric teenagers celebrating multiple A*s. This year, the images may tell a different story. Radical reforms to GCSEs are widely predicted to produce disappointment, and many teenagers are bracing themselves for the worst.

Parents may be unsympathetic, however, if their 15- or 16-year-old spent the exam year ignoring all their wise advice to revise, and instead lay in bed until lunchtime and partied all night with friends. Even if the exam results turn out to be good, many will wonder why their teenager took so many risks with their future.

Sarah-Jayne Blakemore looks barely older than a teenager herself. The award-winning professor of cognitive neuroscience at University College London is, in fact, 44 and has made the study of the adolescent brain her life’s work. She has been critical of the very existence of GCSEs, arguing that they impose “enormous stress” on teenagers at a time when their brains are going through huge change.

“Until about 15 or 20 years ago,” she says, “we just didn’t know that the brain develops at all within the teenage years.” Until then, it was assumed that teenage behaviour was almost entirely down to hormonal changes in puberty, but brain scans and psychological experiments have now found that adolescence is a critical period of neurological change, much of which is responsible for the unique characteristics of adolescent behaviour. Far from being a defective or inferior version of an adult brain, the adolescent mind is both unique and – to Blakemore – beautiful. “Teenagers,” she says tenderly, “are brilliant.”

Blakemore: ‘Teenagers are brilliant’ Photograph: Graeme Robertson/The Guardian

I had always assumed that what we think of as teenage behaviour is largely an invention of contemporary western society. I hadn’t imagined, for example, that 15-year-olds in the Kalahari desert also complain about having to get up early. “But,” Blakemore grins, “actually, they do.” Our ignorance inspired her to write Inventing Ourselves, a fascinating book that explains the science of everything from why teenagers can’t get out of bed in the morning to why they can sometimes appear to be irresponsible narcissists.

“Teenagers get a really bad rap and we mock them and demonise them more than we do any other section of society. And it’s not right. They’re going through an important stage of their development that they need to go through. Most parents don’t know that their teenagers are undergoing such a transformation.”

Blakemore likes to talk about her work by beginning with a quote from a teenager’s diary dated 20 July 1969: “I went to arts centre (by myself!) in yellow cords and blouse. Ian there but didn’t speak to me. Got rhyme put in my handbag from someone who’s apparently got a crush on me. It’s Nicholas I think. UGH. Man Landed on moon.”

What may look to us like jaw-dropping self-absorption is, she explains, in fact essential neurological development, because the biological function of adolescence is the creation of a sense of self. Teens achieve this through creating new allegiances, independent of their parents – which is why their friendships suddenly become so viscerally important. What is known on social media as Fomo – fear of missing out – may look like an irrational sense of priorities, if it means skipping revision to attend a bog-standard party. But when nothing matters more than the approval of their peers, “That brings with it a hypersensitivity to being excluded by friends”.

Blakemore proved this hypersensitivity with an experiment in which adolescents were asked to play an online game of catch, with what they believed to be two other players of their own age. In fact, the game was with a computer programmed to exclude the participants, who found themselves watching the ball being passed between two players on the screen who chose not to include them. She repeated the experiment with adults, and found that while the game lowered the mood and increased the anxiety levels of all participants, the effect was dramatically greater for the teenagers.

It is this hypersensitivity to social exclusion that chiefly, she says, explains adolescent risk-taking. Contrary to popular opinion, teenagers are neither poor at assessing risk, nor prone to believing themselves invincible. “They’re not. Studies consistently show that they get it. They’re really indoctrinated about risks like smoking and drinking and drugs and unsafe sex. But in the heat of the moment, when they’re with their friends, and their friends are smoking or drinking or whatever, it’s incredibly hard for them to resist.” She cites a video game devised by a psychologist, in which the player drives a car and must decide what risks to take at traffic lights. When watched by their friends, adolescents took almost three times as many risks as when alone; in adults, the presence of friends had no impact on risk-taking. Teens’ susceptibility to peer pressure is not, in other words, a character flaw, but a neurological drive.

Acute self-consciousness is another consequence of teens’ preoccupation with peer approval. The term “imaginary audience” was coined by a psychologist in the 1960s to describe the phenomenon whereby adolescents imagine others are constantly observing and judging them. Parents fret about their teenagers’ obsession with social media and selfies, but Blakemore says it is only the logical consequence of technology making their imaginary audience real. “So I don’t think there’s much point in trying to eradicate it. It’s not going to stop.”

Likewise, we should stop worrying about teenagers wanting to sleep in all morning. Our circadian rhythms are determined by a part of the brain that regulates the synthesis of melatonin, but, after puberty, melatonin begins to be produced later at night, which explains why adolescents feel wide awake until late in the evening and find it so hard to get up in the morning. To regard them as lazy is as illogical and unfair as it would be to consider a two-year-old workshy for needing a midday nap. And yet, unlike toddlers’ sleep patterns, the particular needs of teenagers’ are largely ignored.

I am curious about the public policy implications of Blakemore’s work. Were she in charge of the country, what would she change? For a start, she says, we could harness the “pro-social” potential of adolescent peer pressure. “There’s a lot of evidence that teenagers value other teenagers’ views more than adults’ views. There have been studies on bullying – and smoking – showing that if you get the young people themselves to run campaigns, they have a much bigger affect on attitudes than if the same campaigns are carried out by teachers.”

‘I’m a real advocate for teenagers.’ Photograph: Graeme Robertson/The Guardian

She is also interested in the decision some countries have made to ban young drivers from carrying passengers. “Over the age of 25, people drive more carefully when carrying passengers, whereas dangerous driving in young people is most likely to happen when they have got their friends with them.” She mentions, too, a London secondary school that has altered its hours to accommodate its pupils’ sleep patterns. “Which is interesting. We should probably pay attention to that.”

Blakemore is reluctant, however, to stray too far from science into polemic, even at a personal – let alone policy – level. Parents are forever asking her for advice. “But I’m not a parenting expert!” she protests. “I’m really not, so I just can’t do it. My eldest son is now a teenager, but he wasn’t when I wrote the book, so really I have no idea.”

She will concede, though, that her work does inform the parenting of her two sons. When her eldest has a classically adolescent outburst, for example, instead of reacting to it, she tries to picture the inside of his brain. “And I find that useful. A bit like the way you read those parenting manuals when you have toddlers, and they’re all like: ‘Toddlers are just testing boundaries, and their thoughts are more sophisticated than their ability to articulate.’ That does help a bit, doesn’t it, when you’re dealing with a toddler on the floor of Boots.” When she recently made a visit to her eldest’s school, he asked her to pretend not to know him. “I could have been so offended by that; I could have felt really disowned by him. But I didn’t. I thought: ‘That’s absolutely normal, and that’s exactly right.’”

Teenagers’ limitless propensity for embarrassment may sometimes seem bizarre, she acknowledges, but it makes perfect sense. Like most adults thrust on to a stage, teenagers who believe in their imaginary audience want nothing more than to blend into the wings – and Blakemore’s work has helped her make sense of her own blushing teenage self.

She is the daughter of Colin Blakemore, an Oxford university neurobiologist famously targeted by violent animal rights activists in the 80s for his experimentation on animals. “They were hanging around outside our house, threatening to kidnap us, sending us bombs.” The terrifying onslaught against the family and their home endured for more than a decade – and yet, smiles Blakemore ruefully, “The biggest emotion I had was, I was so embarrassed. At school there would be bomb scares Everybody would know it was possibly targeted towards us, and that was just devastatingly embarrassing. And with other teenagers at the time, I was like: ‘Oh God, maybe they’re animal rights, and that’s so embarrassing, because they might be judging me because of this.’ It was just a whole litany of mortification and embarrassment. That was my main feeling about it all.”

What makes Blakemore’s affection and admiration for teenagers so striking, I realise, is its rarity. “I’m a champion of them, I totally am, yes,” she agrees. “I’m a real advocate for teenagers.” Why does she think so many other adults feel differently? She looks suddenly pensive.

“I do often think about why it is that we find it hilarious to mock teenagers, and why there are whole comedy shows laughing at teenage behaviour. I wonder whether it’s because, as a society, we find it really hard that our little children stop wanting to be with us all the time, and wanting to hold our hand in public, and doing more or less what we say.

“That’s not what teenagers do. And it’s really important that they don’t, because they have to become independent from us – so there has to be a lot of rebellion, and embarrassment in front of us, and it’s all part of what’s important for teenagers to do. But that’s really hard for parents to take. And I think that’s reflected in society this sneering we do about teenagers.”

It is our way of coping with their rejection? “Yes.” She smiles sadly. “It’s a way to deal with it, isn’t it? By taking the piss out of them.”