I had just emerged from my own teenage years when I first read Joan Didion’s essay On Keeping a Notebook. Two sentences earned a mark in pen: “I think we are well advised to keep on nodding terms with the people we used to be, whether we find them attractive company or not. Otherwise they turn up unannounced and surprise us, come hammering on the mind’s door at 4am of a bad night and demand to know who deserted them, who betrayed them, who is going to make amends.”

We grow estranged from our younger selves at our peril. This warning sits at the centre of Lucy Foulkes’s excellent and insightful new book, Coming of Age: How Adolescence Shapes Us. Making space for the pain, mistakes and even trauma from the past is essential for our self-perception as adults, even if it may seem safer to edit them out. You also may miss the pleasure and fun of it too.

While Foulkes’s first book – What Mental Illness Really Is… (And What It Isn’t) – focused on how the brain can go wrong, Coming of Age turns to the diversity of normal stresses and pleasures when growing up, plotting out harmful as well as helpful transitions into adulthood. It’s not a book specifically aimed at teens and instead speaks to adults who may still – years later – be coming to terms with their adolescence, while possibly helping their own children through the same murky waters. As an academic psychologist at Oxford University who has been studying adolescent cognition for more than a decade, Foulkes is steeped in knowledge about, as well as respect for, teenage life. She expertly marshals clinical research, both classic texts and recent findings, interlaced with moving accounts from people recruited via social media who open up about their formative years.

It’s worth getting adolescence right because it doesn’t ever go away. Evidence points to a “reminiscence bump” – with the teenage years bang in the middle of it – when memories are notably vivid and in retrospect seem especially significant. This finding holds whether a person is recalling the “landmines” of crisis or memories of intense joy, and is “thanks to the extensive neurological and cognitive development kicked off by puberty”. Foulkes explores how the teens are prominent as a period of firsts – from first love, testing out drink and drugs, to coping with grief – while also opening opportunities to try on identities in the hunt to find out who we truly are.

Despite this period of intensive transition, Foulkes is interested how socially conservative teenagers are. Sex and gender norms matter acutely to them, and sticking to stereotypes about femininity and masculinity is highly prized and tightly policed by a “society of peers”. Sportiness and generic attractiveness afford high status; intelligence, introversion and caution do not. The chapter on “The paradox of popularity”, which examines the dynamics of every school’s cool group (at mine, they called themselves “the posse”, envied and disliked in equal measure), will make readers, no matter where they stood in the social pecking order, collectively clench. With growing recognition of neurodiversity, fluid sexuality and gender identities, high school strangleholds are loosening but only slightly and slowly. Not fitting in, whether by choice or by circumstance, comes at a high price.

Foulkes wants to rehabilitate adolescence and encourage society not to deride teenage traits of self-consciousness, sensation-seeking, risk-taking and laziness, which have evolutionary, physiological and pro-social purposes. They are features, not bugs, underscored by reason rather than pure hedonism. Caring intensely about how we are seen allows us to “develop independence while fitting in with and being protected by a tribe”, she argues. Foulkes is also suspicious of teenagers’ assumed vulnerability to “peer pressure” and the notion that a handful of young people are a “bad influence”, convenient as these excuses may be for parents to exonerate their own children. In fact, most teens are aware of the company they keep, choose it and consent to the activities that are favoured by their friends. Parents would do well to normalise their teenagers’ attraction to the unknown, to testing boundaries and to exploring their sexuality.

Coming of Age concludes that teenagers “have always been utterly underestimated” and focuses on features of adolescence that transcend our cultural moment. But Foulkes perhaps underplays the ways in which modern teens have a substantively different experience to previous generations. Historically, the recognised social phenomenon of adolescence is less than 150 years old. Today’s social media and phone use is changing attention spans, access to extreme content and ideology is readily available and cameras in everyone’s pockets drive self-consciousness. The photographic record of today’s teens will also fundamentally affect how they remember.

As a millennial, I have one box of photos from my life before 20 and not a single selfie. Smartphone teens, meanwhile, will live under an oppressive weight of primary sources. Foulkes doesn’t tie her analysis to current affairs, but it’s impossible not to make connections with our political and social moment. How can the Covid lockdown years ever be repaid to people now in their early 20s? Why is there not more research across disciplines into the teenage experience? If adolescence matters so much – and you cannot help but agree that it does after reading this book – why is it scarcely visible in healthcare and society?

Foulkes remains offstage in Coming of Age. She admits that she considered sharing stories from her own life, but chose instead to foreground her interviewees. I sympathise with the clinical and researcher instinct to step back, but it feels important as a reader to know the younger person with whom Foulkes is trying to remain on nodding terms (a person who struggled with mental health difficulties, of which she talks more about in her first book). Her example, her authority, might have shown in action the brave, rewarding process of reflecting on and retelling your own past.

Thinking of what has happened to us as a story for which we are a (more or less unreliable) narrator gives meaning and agency to our lives. It is also a constituent of lifelong mental health. It’s not a story we tell just once, though. In notebooks, real ones or the sketchpad of our memory, we revise these stories, a process that can be supported and structured through therapy. A therapist can guide people to unseen redemptive possibility and to find closure. A gentler, amused and curious disposition about the people we used to be allows our minds to become saner places to live. We’ll also think better of those young people whose adolescent notebooks are still unfinished first drafts, who could benefit from the hope that everything is (probably) going to be OK.

Kate Womersley is a doctor and academic specialising in psychiatry. Her work at Imperial College London focuses on sex and gender equity in biomedical research

• Coming of Age: How Adolescence Shapes Us by Lucy Foulkes is published by Bodley Head (£22). To support the Guardian and Observer order your copy at guardianbookshop.com. Delivery charges may apply