The answer should lie in more than the mere convenience of busy, middle-class parents, John Rae, former headteacher of Westminster School, told a recent symposium on boarding. If it did not, boarding would not survive.
Searching for an answer - and for ways to make boarding better - were 40 heads, housemasters and housemistresses gathered at Milton Abbey school in Dorset, an 18th- century mansion with medieval abbey in a Capability Brown landscape that, in 1954, became one of the newest public schools.
The speakers ranged from a former prison governor to a specialist on intensive farming techniques.
What had sustained boarding schools for so long was the belief that they provided something special in the form of that much-abused concept of "character", Dr Rae said; honour, decency, loyalty, placing team before self, stiffening the upper lip when necessary. Now that belief was dead and had not been replaced.
Jonathan Hughes-D'Aeth, headteacher of Milton Abbey and inspirer of the symposium, had a very 1990s version of "character" to propose: citizenship.Better boarding made better citizens, he said.
"Society is becoming ever more fragmented," said Mr Hughes-D'Aeth. "GameBoys, computers, television are freezing the power of speech and stunting social skills. Boarding schools buck this trend. Living together necessitates communication, consideration for others. This is why everyone would benefit from a spell of residential education."
Dr Rae said many boarding schools, especially for girls, were in the top 100 in league tables, although they could not be as selective as day schools. The reason must lie not just in good teaching but in some "extra ingredient".
Peter Barnet, warden of the Pilsdon Community in Dorset, considered it essential to get away from the elitism and snobbery in boarding schools if they were to make a contribution to the life of the nation.
The image of boarding is still tarnished by horror stories of fagging and bullying. There was no shortage of these at the symposium.
Christopher Vlasto, who was at prep school and then Charterhouse in the 1950s and 1960s and who is now a psychotherapist working with "boarding school survivors", described the abandonment and desolation he had experienced - and the terror induced by a headteacher whose voice alone had made him wet himself.
But all present agreed that it was time to stop dragging themselves back to the brutal past. Boarding schools had changed.
Gillian du Charme, head of the girls Benenden School, said boarding was now fun. Not only that, boarding schools contained some of the best educational practice in the country. The only way to keep boarding schools alive, she said was "be ever more wonderful".
One member of the audience was still troubled by something. Was boarding school the best place for 12 to 18-year-olds to develop their sexual identity?
"It's quite possible - but in a co-educational school," was the reply from the deputy head of a mixed boarding school. "And animals are helpful," added Peter Barnet.