I once knew an American psychoanalyst who worked in a Bangkok practice, specialising in expats. He’d first come to east Asia on contract for an international church whose missionaries kept getting into trouble. He never went home: there was more than enough work. “Specifically,” he said, “with people like you. Middle-aged, middle-class Brits who went to your crazy private schools may just about be the most damaged social sub-group I’ve ever come across.”

It’s long been known that the practice of sending young children off into the care of strangers is not wholly safe. The ancient “public” schools worried the Victorians as much or more than did the workhouses: three parliamentary commissions sat in the 19th century to look at the financial frauds, riots and the astonishing numbers of deaths – from suicides, assaults by teachers and pupils, starvation, epidemics – in the schools of the rich. Tom Brown’s Schooldays only scraped the surface.

In the 20th century a clutch of authors, from George Orwell to Roald Dahl, wrote in their different ways about the systemic cruelty, psychological and physical, and of its wider effects. One of those was the establishment of the principle, among the elite and the ordinary, that to have been brutalised at a boarding school was key to becoming the right sort of Briton – one that might run an empire or a corporation, or a cricket team. Naturally, as the proven best way to educate a ruling caste, the system spread across the English-speaking world.

Psychology seems to have taken a long time to catch up with the issue, perhaps because Freud famously dismissed most of his child patients’ allegations of abuse by adults as fantasy. Given the importance the boarding-school class had and still has in running modern Britain – from the City to Westminster, not forgetting the BBC – that seems to have been an omission. Joy Schaverien coined the term “boarding school syndrome” only a decade ago, though she follows in the footsteps of Nick Duffell, a psychotherapist who started work in the field in 1990 and wrote a passionate and influential book about the wounds boarding can inflict, The Making of Them.

Duffell is himself a “boarding school survivor” – his own term – and that inevitably fuels his work. But Schaverien, a Jungian psychoanalyst, did not go to boarding school: it was as a practitioner that she became intrigued, noting how often boarding school featured in the past of surprising numbers of her patients. That makes her book – an academic work, academically priced, though a gripping read – all the more important. There’s a confused debate going on about private boarding schools, with arguments about class and unfair privilege mixed up with a bewildering range of notions about children’s emotional health. Schaverien brings a clear eye and the experience of 25 years of collecting data to an issue that should concern everyone worried about how children fare in professional care – which, of course, is what boarding school is.

She’s not impartial. In Britain, you don’t have to have gone to a private boarding school to be affected by them and their product. Schaverien’s experience comes from her father, who, in old age, told his family how he still ached at memories of being left at his boarding school in Brighton, in 1916, aged six. The fact that he arrived in short trousers and wearing a velour hat with elastic under the chin ensured that he was savagely bullied from the first minute. “If I was so precious that mother dressed me this way, why then did she part with me?” he was still wondering, 70 years later.

That’s by no means the most upsetting story to be found in Schaverien’s awful case studies. But it does go to the heart of the issue, both for angry ex-boarders, their spouses and children and anyone bemused by the system. I’ve talked and corresponded with all of those since I started writing for this newspaper about sexual abuse and bullying in British boarding schools, state and private.

The many hundreds of emails I’ve received make it pretty clear that the schools of the elite suffered the same cover-ups and the same astonishing failings in regulation and in policing as did the hospitals, care homes and young offenders’ prisons. The difference? As several correspondents put it, in anger or amusement, “Posh people’s parents paid to have them abused.” That, of course, is what most hurt Hymie Schaverien, and thousands of others. “Boarders cannot console themselves with the thought that their parents did not want them to go,” Professor Schaverien states. Their parents chose to send them from home into hell or prison – words her patients frequently use – and so to break the bond with their child.

Attachment – the crucial establishment of trust and security through a primary carer – is the basis of modern child development psychology. Boarding schools could not have broken or redirected healthy attachment more effectively, as Schaverien illustrates. From the moment the parent drove away, a child had to adjust to the fact that not only was privacy and safety no longer guaranteed – let alone the consolation of a hug – but that their parents had chosen this future. John Bowlby, the psychologist famous for first coming up with attachment theory in the 1960s, described public school as part of “the time-honoured barbarism required to produce English gentlemen”. Bowlby boarded at 13: he was against it.

Schaverien has, of course, accounts of children who enjoyed boarding school: though some patients inform her that that was because home life was so deficient in love or structure that the necessary attachments were better made at school. It’s hard not to conclude that boarding schools were meant to do this job: replace infantile loyalties to mummy with the bonds that tie you to the team.

It worked: but the side-effects of this abrupt intervention in a six- or eight-year-old’s development could be savage. Symptoms that a therapist in boarding school syndrome addresses are problems with anger, depression, anxiety, failure to sustain relationships, fear of abandonment, substance abuse and so forth. A common effect is amnesia: many of Schaverien’s patients – and my correspondents – have sad gaps where, in a normal childhood and adolescence, there would be a wealth of memory. Forgetting the pain is yet another coping mechanism.

In a fascinating account of four years’ analysis with one deeply traumatised patient, Theo, Schaverien takes us to the point where she believes boarding school syndrome is born. On the way we see Theo – often using drawings – recover memories of awful injustice. That is a key issue for many boarders – children, she says, have an ethical sensibility from an early age and it is traumatic when something – like brutality on the part of an adult – violates it. Trauma affects the normal development of a child’s brain.

Eventually, and in Theo’s case this happened dramatically, a traumatised child, exhausted by perpetual fear, may be forced for their own survival to separate their selves – the normal, vulnerable home self, and the boarding-school self. That’s the syndrome, and though sceptics of Jungian theory may be dubious, my correspondence has many people who talk unhappily of the child they left behind at the school, their other self who was never able to grow up. It’s a profound effect, an “encapsulation of self… that may last a lifetime”, Schaverien says.

It’s obvious enough that these institutions, full of emotionally needy and incompetently supervised children, have provided havens and hunting grounds for sexual criminals since their beginning. Hence the extraordinary wave of allegations about historic child abuse in institutions. Schaverien devotes an interesting chapter to sexual abuse but, for her, it is not the main issue. Theo never experienced sexual abuse.

It grabs the headlines, but I suspect that for those who want truly to protect and succour healthy children, the shocking revelations about paedophiles in institutions may be a distraction. Again, while my correspondence contains many awful allegations, it’s also full of people apologising for not having a story of sexual predation to tell. “It was only bullying,” people write, “not what you’d call abuse.”

But emotional cruelty is what exacts the greatest toll on the developing mind. Children are resilient, they can recover from physical hurt: it’s clear from reading Schaverien that what most reliably damages children is long-term emotional neglect, the absence of safety, the failure of justice, the loss of love. We need the psychological abuse of children to be properly outlawed – a long-awaited “Cinderella law” came into force last month, but it is weak – and we need to ask the rich and aspirational to think again before they put their children into care. They should read this book: it could save them a lot of money.

Boarding School Syndrome is published by Routledge (£27.99). Click here to order it with free UK p&p