A HUNDRED YEARS AGO the question of what makes a classic must have seemed easy.

In Elizabeth Goudge’s novel Henrietta’s House the heroine is asked to choose the perfect library for a girl of her age. Into it go The Water Babies and Alice in Wonderland, Undine and The Pilgrim’s Progress, Jackanapes and Little Women, The Fairchild Family, A Flat Iron for a Farthing, The Back of the North Wind, The Princess and Curdie, Andersen’s Fairy Tales, The Swiss Family Robinson, Andrew Lang’s Blue Fairy Book, Lob Lie-by-the-Fire, Treasure Island and The Cockyolly Bird.

Most of us would have heard of only half these titles, and only Alice in Wonderland and Little Womenare at all likely to be read by children today.

If you were to look through the catalogue of books reprinted by Everyman’s Library, you would have another list. This month it has completed a donation of £20 million worth of books to give to more than 4,000 state secondary schools, a munificent gift aided by the Millennium Fund. These 300 books are not children’s classics but adult ones, ranging from Pride and Prejudice to more obscure authors such as Chinua Achebe and Mikhail Bulgakov.

This raises the question, though, whether they will appeal to children. Everyman’s publisher, David Campbell, knows that a handful of school librarians have rejected the gift because they thought children would find them unattractive. He thinks that they will be read mostly by sixth formers, not under12s.

“The point is not to help children to read,” he says.

“There are lots of paperbacks and pick-me-up books and manga comics that do that. I want these books, which are the DNA of our culture, to be accessible to children in a form that will last 100 years or more. If just one child in a bookless family has his or her life changed, it has been something worth doing.”

Adults adore Everyman and treasure its restrained format, quality paper and gorgeous endpapers. The idea of teenagers discovering classics through such beautiful editions is entirely laudable. Yet my own children, both avid readers of classic fiction, have yet to open a single Everyman edition, because they find them “repulsively posh”. This view is echoed by Francis Gilbert, the author and secondary school teacher.

“Most pupils of mine would run a mile before picking up an Everyman; this is partly because the content is often too difficult for them to read in one continuous gulp, and partly because the books are so dryly presented. I’d break them down into small books with more interesting covers, provide plenty of notes and pictures, and generally focus on the texts that pupils are bound to like: for instance, The Miller’s Tale, by Chaucer, certain short stories by writers such as Poe, James and Dickens.”

There is also the perennial problem of what books are indisputable classics, Whether the Harry Potter series will survive remains contested; the status of Philip Pullman's His Dark Materials is not. Perhaps the only instantly identifiable modern work of classic fiction, it is a tale that can be enjoyed by both child and adult readers.

Pullman’s publisher, David Fickling, agrees that “nothing is totally independent of fashion” but says that his definition of a classic is “rereadability”. “Plenty of books are enjoyable to read once, but with a classic, the more you reread, the more comes out. It’s the same for all ages; there is that tone, that care with words, that control from the big picture down to individual sentences.”

David Campbell describes a classic in Dr Johnson’s terms as “a book that more than one generation has agreed has classic status”; he points out that while 95 per cent of books ever published are out of print within 100 years, Marcus Aurelius and Virgil have lasted more than two millennia.

Yet great books do fall out of print, especially where children are concerned, and classic status fluctuates according to chance as much as taste. The publisher Jane Nissen, who has rescued lost classics, from Alison Uttley’s A Country Child to Eric Linklater’s The Wind on the Moon, says: “To me, a classic children’s book is one that ignores the passage of time. What such a book has to say is so compelling, important, affecting and amusing that the reader is irresistibly drawn to it and a bond is forged. Classics from the past retain their meaning and power — and the classics of the future will do the same.”

In our own lifetime we are lucky to encounter even one or two new novels that have this impact. Everyman’s Library includes one or two recent novels such as Penelope Fitzgerald’s The Blue Flower, and Isabel Allende’s The House of Spirits,which one suspects will not be read in a generation as anything but a historical curiosity. Yet the rest will remain, a blessing to each passing generation — whatever the form in which they are encountered.

Times Recommends

• The 100 Best Books of the Decade
• The Times picks the 50 best paperbacks of 2009
• The conversation: James Ellroy