When Amy Newsham went to the Hay-on-Wye literary festival this year, she found herself surrounded by the usual mix of publishers, agents and chattering literati. And then there were the teenagers dressed as semi-angelic humans, with runic symbols emblazoned across their arms and chests.

The teenagers were there to hear a talk given by young-adult author Cassandra Clare. Newsham was one of the few fans of Clare’s six-part fantasy series, The Mortal Instruments, over the age of 20. And she was one of the few fans not dressed as one of the novel’s characters, complete with henna tattoos.

“They were properly kitted out,” says Newsham, key stage 3 leader in English at Cardinal Allen Catholic High School in the North West of England. “It was mad. They’d obviously read everything about the books and the author - feasted on it - so that they could be the most knowledgeable fan.

“It was very bizarre to witness an author have that effect. There were hours of queues to get an autograph from her. It was mad. But it’s also really good, because it shows that teenagers are reading.”

As any recipient of the “whatever” shrug can attest, teenage interest is a hard-won thing. But once it has been won, it will stick around with the loyalty of a particularly grateful Labrador. And so teenage readers are cleaving to multiple-novel series with the unshakeable devotion that previous generations reserved for religion. Recent breakout successes in children’s fiction include the four Twilight books, the three Hunger Games novels and, of course, the seven Harry Potter sagas.

Out of this world

“I remember reading Jacqueline Wilson until it came out of my earhole,” Newsham says. “I read Jacqueline Wilson again and again and again. I read Harry Potter again and again and again. Whenever a Harry Potter book came out, I’d start from the beginning and reread them all. There’s something of an almost obsessive, compulsive nature about series, isn’t there? There’s a whole world created that you want to be a part of, that you want to witness.”

And, she says, her students today are increasingly treating series of novels with a reverence previously reserved for music or film. Their authors, meanwhile, have become full-scale celebrities.

“While there are teen books that come out of nowhere and do really well, there are quite a few big authors who basically dominate the best-sellers at the moment,” says Melissa Cox, children’s buyer for bookselling chain Waterstones. She names Clare’s The Mortal Instruments, but also Veronica Roth’s Divergent fantasy trilogy, the first book of which has just been made into a film.

“The magical fantasy world is the appeal,” Newsham says. “But there’s also something that’s tangible to their lives, as well. It’s something that’s different to what they know, but it’s also similar to what they know.”

The Mortal Instruments, for example, is set in New York City. Its heroine is a normal teenage girl, growing up in a normal family, until she suddenly discovers that she has access to a parallel demon world. Similarly, the Divergent series is set in a post-apocalyptic - and yet recognisable - version of Chicago.

“There’s the element of fantasy, but there’s realism in there as well,” Newsham says. “They’re in touch, but also out of touch, with students’ everyday lives.”

This is the key, says Ruth Alltimes, publishing director for HarperCollins children’s fiction. Teenagers are not automatically predisposed to like every book featuring a vampire or a rune-sporting semi-angel. “There are some books that are so very much concept-driven that they don’t focus on character,” Alltimes says. “And they’re the ones that didn’t take off as much as Hunger Games or the Divergent trilogy.

“It has to have an emotional heart. There has to be some emotional core that works all through the book. Sometimes that’s a love story, but not always.”

Despite their demon-fighting tendencies, the female protagonists of these novels are essentially everygirl.

“They tend to be very ordinary,” Newsham says. “Throughout the series, they develop into women - into a heroine. In The Mortal Instruments, she has to deal with being a teenager and having a mum who wants to know where she is all the time. But then she also goes out and fights demons.

“That transition from teen to young woman is something students like to see. You come from nothing, and you’ve achieved certain things, and you can fight demons.”

Lacking bite

Newsham takes her task sufficiently seriously to make the ultimate sacrifice: she has dutifully ploughed through all four Twilight novels. This, in case any readers have been locked in a stationery cupboard for the past few years, is the shockingly written vampire high-school love story (sample line: ” `Sshh,’ he shushed me”) that involves characters brooding about all the sex they are failing to have.

“Bella really irritated me,” says Newsham of Twilight’s narrator. “I wanted to punch her in the face on several occasions. She’s constantly whining about being in love - she’s not a strong character to present to teenagers.”

But, says Alltimes, even Twilight offered teenagers something they could relate to. “There’s a lot of angsting and yearning for each other’s bodies in Twilight,” she says. “Teenagers are packed with hormones, so of course they like to read about emotional situations.”

Trends, of course, are notoriously mutable: they follow a clear pattern right up until the unpredictable happens. So teachers returning to school in the autumn are likely to find their students less obsessed with books about vampires, angels and dystopian worlds, and instead reading about the traumas of teenage cancer, the death of a parent or the suicide of a friend.

But this is less of a leap between dystopian realities than it might at first appear, Alltimes argues. “There’s definitely been a shift towards contemporary and real-world books,” she says. “The angst of something like Twilight and Hunger Games is being translated into books dealing with very heightened emotional situations that are real. But now it’s about coping with death rather than making out with a vampire.”

A safe space

In part, this is a result of the massive success of John Green. Green’s first novel, Looking for Alaska, tells the story of a teenage girl whose mother died when she was 8 and who ultimately ends up killing herself. His most recent book, The Fault in Our Stars, is about a 16-year-old cancer patient. The novel entered the New York Times best-seller list at number one when it was published in January 2012. A film version has just been released.

“Think how influential Judy Blume’s books were, 10, 15, 20 years ago,” says Kate Wilson, managing director of Nosy Crow children’s publisher. “They occupied the space that John Green does now: realistic pain by proxy. And these stories are parent-free. They’re very much respectful of the autonomous teenage experience.”

And such books allow teenagers to think about illness, death and suicide, without awkwardness or fear, Newsham says. After all, she points out, if a student started asking her questions about suicide, she would be obliged to report the conversation.

“When you’re a teenager, you’re in a weird position,” she says. “You’re not a child any more but you’re not an adult. You don’t have the emotional confidence to understand these issues, but you want to understand them.

“They’re such awkward, difficult topics to broach and understand. Literature is very powerful in that way: it tells you about these things without patronising you. It also develops teenagers’ emotional intelligence and it doesn’t judge them.”

Waterstones’ Cox predicts that Rainbow Rowell, US author of Eleanor amp; Park and Fangirl, will appeal to the John Green demographic: Rowell already has praise from Green on the cover of one of her novels. “She’s got the same momentum as John Green before he was a big star,” Cox says. “I’d put my money on her being the next big thing.”

Another recent word-of-playground-mouth success is the Geek Girl series by Holly Smale, in which a geeky schoolgirl is spotted by a modelling agent and whisked into the world of high fashion. A third book has just been published.

In many ways, Alltimes says, Geek Girl panders to the same wish-fulfilment fantasies as series such as Divergent or The Mortal Instruments. “It’s real-world,” she says. “It’s a girl who’s a bit geeky, but who also gets the dream of being a catwalk model. Every girl feels like she could be her.”

Authentic voices

Among younger readers, meanwhile, the angst-filled world of Jacqueline Wilson retains its appeal. And in September, the Harry Potter books will be reissued with new covers and illustrated text. “It’s a totally different reading experience, seeing the text swathed in all these different images,” Cox says.

The aim is to bring the Potter stories to new, younger readers, who may have seen the films but have yet to read the books. But although the novels themselves may not be as ubiquitous as once they were, their effect has endured.

The success of Harry Potter revitalised the boarding-school story, opening the school gates for more to follow. One of the biggest children’s publishing debuts of last year was The School for Good and Evil by Soman Chainani, the first in a trilogy set in a school that teaches fairy-tale heroes and villains.

“It was a playground hit,” says Nosy Crow’s Wilson. “Boarding-school stories are just perennial stories. If you can get it right, children are really, really responsive to that.”

Cox agrees. “School stories loom large in your childhood and your teenage years,” she says. “A lot of your time is spent at school and it’s where a lot of your life happens. A lot of contemporary fiction inevitably has to feature school and school surroundings, because that’s where children are so much of the time.”

Such books are particularly reliant on the author’s ability to recreate school life authentically. Nosy Crow has published two school stories - Baby Aliens Got My Teacher and The Spy Who Loved School Dinners - by philosophy teacher Pamela Butchart. Several other authors on their list are also teachers.

“I think getting the voice right is the most important thing,” Cox says. “Teenagers can tell immediately if people are writing a teenage voice that doesn’t sound like an actual teenager.”

This is echoed by Alltimes, who will publish Solitaire, by 19-year-old Alice Oseman, in August. “She’s fresh out of that world, so she writes the young adult perspective really well,” Alltimes says.

The internet is full of fan fiction, often written by teenagers themselves, and young adult readers therefore expect their narrators to sound as though they have stepped straight from the playground. “Obviously, as publishers we have to curate the market,” Alltimes says. “But what the writing needs to have is an authenticity. Sometimes, authors err on the side of being too earnest, writing how they think teens should be rather than how they are.”

This authenticity is therefore one of the key elements that editors look out for when reading new manuscripts. “Teens and young adults are the fastest to sniff a whiff of anything condescending, try-hard, patronising,” Alltimes says. “It has to be really real.”

But a reader’s experience of a book, inevitably, also comes down to personal taste. “I’ve got some students who just read John Green books,” Newsham says. “I’ve got another student who just reads fantasy books. I’ve got some students who read both.”

And, she adds, teenagers may not always have the same tastes as their teachers - even teachers who queue alongside costumed teenagers to hear a fantasy author speak at a literary festival. Newsham, for example, disliked Looking for Alaska because she found the central character selfish and unlikeable. Her students, meanwhile, loved it.

“I couldn’t relate to her because I’m not a teenager any more,” Newsham says. “I come to it from a very adult perspective, whereas they come to it from a very teenage perspective.” She pauses. “Well, they would, wouldn’t they?”

What teenagers will be reading this summer

John Green: The Fault in Our Stars, Looking for Alaska

Death, cancer, drink-driving, bereavement. Also teen sex. Judy Blume for the modern era but without the hideous social shame heaped on anyone called Ralph.

Soman Chainani: The School for Good and Evil series

Every four years, two children are taken from the village of Gavaldon: one to be enrolled in the School for Good, which prepares children to become fairy-tale heroes, the other in the School for Evil, which trains them to be fairy-tale villains. Harry Potter meets Clueless.

Rainbow Rowell: Eleanor amp; Park, Fangirl

Eleanor amp; Park is about comics and mix tapes, with racist bullying and domestic abuse thrown in for good measure. Fangirl is a story about twins, first love and fan fiction. It includes a fictional novelist called Simon Snow, whose novels are a homage to Harry Potter. Teen fiction will eat itself.

Holly Smale: Geek Girl series

Harriet Manners is a geek. She knows that bats always turn left when exiting a cave and that peanuts are an ingredient in dynamite. No one at school likes her. Harriet is spotted by a model agent and tries to reinvent herself. If a kindly adult had simply told her a) that her time would come at university and b) about the existence of pub quizzes, she might have been spared a lot of angst.

Cassandra Clare: The Mortal Instruments series

A thousand years ago, the angel Raziel mixed his blood with that of humans and created a race of human-angel hybrids, called Nephilim. These Nephilim, or Shadowhunters, protect the world from interdimensional demons bent on destruction. A bit like Buffy the Vampire Slayer, but with tattoos.

Veronica Roth: Divergent trilogy

Here’s what Wikipedia says: “Beatrice, an Abnegation born and Dauntless transfer, must figure out her life as a Divergent.” The film of the first novel in the series was released in April, so most teenagers ought to be able to translate that for you.