By his own account, Tim had a pretty conventional upbringing. He had a stable childhood and lived in relative harmony with his parents and two brothers. Even when he came out as gay it caused barely a ripple: he was fine with it, his parents didn't make a fuss and his friends accepted it.
It was when 14-year-old Tim accepted an offer from a friend that his life started to veer off course. In normal circumstances his natural suspicions would have led him to say no, but he was going through a period of depression and low self-esteem. His friend's way of cheering him up came at just the wrong time.
"He had met this guy off the internet and he would go round to his flat and he gave him drink and cigarettes," Tim recalls. "I was feeling a bit low so he asked if I fancied going round."
The pair went to the flat, where Tim met Paul, who he guessed was in his mid-20s. They watched a DVD, smoked some cigarettes, had a few drinks, then Tim's friend and Paul went into the bedroom. "I knew what was going on," Tim says, "but I didn't get involved."
But he was persuaded to go back, and on his next visit he was talked into accompanying Paul into the bedroom. They had sex, and it was clear this was part of the deal. "It was like a package," Tim says.
The combination of cigarettes, alcohol and the attentions of an older man proved irresistible. "At first I felt quite grown-up," Tim says. "I was 14 and I was smoking, drinking, having a laugh, having sex. I thought this must be what relationships are like.
"When you're 14 you don't have much experience, and if you're gay the chances of having a boyfriend are quite slim, so it was fun."
One evening Tim turned up to find Paul had invited some friends over. It became clear that they, too, were part of the deal. Tim went into the bedroom and had sex with each of them in turn. Pretty soon, Tim was having sex with six or seven men on each visit.
He started to feel it was getting out of control. He said he didn't want to do it any more, but Paul threatened him with violence. He also said if Tim did not turn up, he would go to his house to pick him up. Tim was desperate to prevent his parents finding out what he was up to, and agreed to keep doing it.
After a couple of months, Paul said he wanted Tim to meet some friends in a nearby town. For the next 18 months, Tim was sent all over the south of England to meet Paul's "friends". He was expected to have sex with them, sometimes in groups, sometimes one after the other.
"It was completely out of my control," he says. "I wasn't choosing to do it - I was forced to do it. As it went on it started to get scary and it got more and more difficult to say no."
He again tried to back out and told Paul he did not want to carry on. A few days later, Tim was walking through his home town late at night when he was attacked by two men. They took him into an alley and raped him, one after the other. One of them left with the parting shot that unless he went back "to do what you used to do", this would happen again. His back still bears the scars from the attack.
At school, Tim had been a conscientious and well-behaved pupil, but he began skipping classes one or two days a week. He was using a lot of drugs and he stopped eating to the extent that, he says, he "looked like a skeleton". He started self-harming, cutting his arms and legs. When he wore his PE kit the marks were clearly visible. No one at school said anything - they simply didn't know how to deal with it, Tim believes.
"Somebody could have picked up on it, but teachers aren't trained to look out for those signs," he says. "I was down all the time and it was obvious something was wrong. I had these scars all over my arms, but no one, not a teacher or a teaching assistant, asked me what was the matter."
Serious cases of child exploitation are uncommon, but recent high-profile cases, such as in Derby, where a gang of men was convicted of grooming and abusing teenage girls from schools throughout the city, have highlighted the role of schools in protecting children and detecting potential abuse.
Schools are a crucial link, according to Anne Marie Carrie, chief executive of children's charity Barnardo's. But she believes victims often go unidentified because of a "lack of awareness" in front-line services, including schools, of the tell-tale signs of abuse.
These include sudden changes in behaviour, truancy among pupils who had previously good attendance records, children becoming secretive or distanced from their friends or turning up at school with unusually expensive clothes or phones.
"People often don't see the signs because they are not looking for them," Ms Carrie says. "Teachers have a critical role: we need them to look out for these changes."
She believes teachers can also help stop young people falling prey to exploitation in the first place. "Schools are a trusted arena where children can have a discussion about grooming and what to look out for," she adds. "There is more we can do to make children safety-aware."
Technology is seen as a key area for prevention work. While children can often take what they see on the internet at face value, social networking, for example, allows would-be exploiters to mask their identity. "Technology is being used to find children in their own homes, isolate them and then control them," says Ms Carrie.
Saltash.net community school has enthusiastically embraced the use of technology in classrooms, with pupils often encouraged to use mobile phones in classes, for example. But alongside this comes a responsibility to promote safe use of technology, says deputy head Dave Garland.
Saltash.net is an ambassador school for the Child Exploitation and Online Protection Centre, a national police agency that promotes e-safety, and has an online reporting mechanism, where pupils can raise issues with staff, and a forum where parents can discuss concerns.
Mr Garland says the school emphasises the dangers of taking online identity on trust, giving strangers access to personal information and putting private details on the web. The advent of smartphones makes it harder for parents to monitor internet use, putting more of the onus on children to keep themselves safe.
"It is about hammering home the message of what is appropriate and what isn't," he says. "It is about recognising when things don't feel right, and knowing the steps to take."
But e-safety is only part of the story. In a recent incident at saltash.net, a 13-year-old girl was befriended by a 19-year-old outside of school and not via the internet. The school's child protection co- ordinator stepped in to point out to the pupil that the relationship was inappropriate.
Wendy Shepherd, who runs a Barnardo's project working with sexually exploited children in Middlesbrough, believes it would be a mistake to concentrate solely on the online risk. "We know that perpetrators will infiltrate groups of young people hanging around on street corners or in parks," she says. "They will often groom them and sexually exploit them by pretending to be their boyfriends."
At Safe and Sound Derby, a charity that specialises in working with young people, around three quarters of the victims of sexual exploitation it sees are not groomed online, according to chief executive Sheila Taylor. Many are either picked up off the street or recruited via their friends. She says the abusers are often highly skilled at insinuating themselves into their victims' lives, using presents and treats to win their confidence. "The men are very sophisticated in their approach," she says.
The case in Derby certainly owed little to the internet. Abid Saddique, 27, and Mohammed Liaqat, 28, were jailed earlier this year for a minimum of 11 and eight years respectively for a series of sexual offences, including aiding and abetting rape. Their trial heard the pair were at the centre of a grooming ring that had preyed on at least 26 girls, some as young as 12, over a two-year period. As well as having sex with the girls themselves, the pair "farmed" them out to others.
Detective Superintendent Debbie Platt of Derbyshire Police, who led the investigation, said most of the victims were picked up off the streets. Schools were particularly targeted by Saddique and Liaqat. "They would cruise around Derby and go to any areas where children would congregate," she says. "So it was school car parks, side-streets next to schools, school gates, as well as parks and shopping centres."
Kevin Murphy, head of education welfare for Derby City Council, says opportunities to expose the sexual exploitation ring earlier were missed when signs were not picked up on and information was not passed on.
"There were girls who, all of a sudden, had poor school attendance or they started coming in with brand new clothes and the latest mobile phones," he says. "There were a lot of clues that went unnoticed and there was a real communication breakdown."
He recognises that some of the signs can be hard to spot when teachers are dealing with classes of 30 children at a time, but says some teachers choose not to acknowledge what is in front of them.
"It is quite a common feeling for teachers that they don't want to know because it is so horrible and if they don't look at it, it will go away," he says.
None of the schools involved in the Derby case has been publicly identified, but one agreed to talk to TES Magazine on condition of anonymity. The school was first alerted to the issue when a pupil told the nurse she had been sexually abused by a gang. A police investigation revealed that a number of girls at the school had been involved, most unbeknown to each other.
The school's assistant head and child protection co-ordinator says long- standing awareness sessions run throughout the school to alert pupils to the dangers of grooming, both online and off. But this was not enough to prevent children from falling victim to the gang. "What we have been through as a school is a completely different ball game," she says. "The only common denominator was all the children were vulnerable, in some shape or form."
Although some of the victims came from troubled family backgrounds, this was not always the case. While some parents did not know where their children were, one girl used to climb out of her window and down the drainpipe to meet her abusers without her parents knowing.
But what most surprised staff was how effectively the children had been groomed. "Some of them still don't believe anything has been done to them," she says. "One girl is madly in love with one of the men and is desperate to have a baby with him."
When told that this man is married and has also abused other girls, her reaction is unequivocal. "He doesn't love them; he loves me," the girl says.
While the school has, not surprisingly, found it hard to work with this girl, sessions with other victims have proved an effective way of getting the message across on the dangers of grooming. "If you work with some then it spreads to the other children," the assistant head says. "Sometimes that is more powerful than when we as teachers tell them something."
She says the school has also stepped up its vigilance in the wake of the revelations. "We're monitoring and watching and checking cameras all the time," she says. "If we're suspicious about the groups the children are in, we will talk to them to try to disperse them."
The city council has launched a training programme for teachers since the grooming ring came to light. "Schools see these kids a lot of the time and they need to take notice of what's going on," says Mr Murphy. "We have to be aware of some of the subtle behaviours that children display. It is about reading the signs and using emotional intelligence."
One issue regularly raised at training sessions is from teachers who say they have enough to do without being expected to be social workers as well. Mr Murphy's response is unequivocal. "If their kids are being abused, teachers will not be able to do their job," he says.
Even if a teacher's suspicions prove groundless, he says voicing them and getting it wrong is far better than the alternative. "All we want is for the teacher at the front of the class to pass information up the hierarchy," he says. "There is no excuse for not passing it on."
Schools also have to take a more nuanced approach to help stop young people falling prey to sexual exploitation in the first place, says Safe and Sound Derby's Ms Taylor. She believes the focus on internet safety has often overshadowed the need to reduce the overall risk.
"People understand online grooming but there is little understanding of other aspects of sexual exploitation," she says. "There is not enough training out there. Clearly online grooming is important, but other areas haven't had that dedicated response."
For Emma, the grooming process began when she was befriended by a gang of older boys in a shopping centre in Derby when she was 12. At first it seemed innocent enough, but when she turned 13 - the age at which the penalty for unlawful sex becomes less severe - she was introduced to a man in his 20s.
"He raped me, but I didn't realise it was rape," she says. "I always thought rape had to be a dirty old man in an anorak. I thought I felt the way I did because I was a virgin and that is how you feel when you lose your virginity."
After that, her "friends" asked her to have sex with a parade of cousins and uncles and brothers and friends. They would pick her up in their cars and take her to flats or a park. "Sometimes it was 10 or 15 men a time," she recalls.
At first, she thought she was having a good time. She got cigarettes, alcohol, cannabis. As it went on, she felt she was no longer in control.
From being a straight-A student, Emma began to skip lessons and became disruptive in class, to the point where she was permanently excluded from school at 14. She believes her school was aware of what was happening, but chose not to intervene.
"They couldn't have me in school because if these men turned up it could put the other kids in danger," she says. "They didn't want it to spread."
Like Tim, it was fear that stopped Emma from bailing out. The gang threatened her and told her they would gang rape her mother and firebomb her house if she did not do what they wanted. "It was easier to shut up and do it."
After two years, Emma escaped. She got rid of the mobile phone the gang had given her and managed to cut off all contact. Now 21, she visits schools with Safe and Sound, to talk to pupils and teachers about her experiences.
"If I had been taught about paedophiles at school when I was first being targeted alarm bells would have started ringing," she says. "But I was never taught anything about it - it was like it didn't exist."
Tim also managed to escape from his abusers' clutches, in his case shortly after his 16th birthday. A friend pointed him towards a Barnardo's project in his home town, where staff helped him cut off contact. Now he was 16, his abusers were less interested and did not pursue him.
Like Emma, he believes that stronger warnings at school could have prevented him from spending two years of his childhood being shunted around the country, forced to have sex with a succession of strangers.
"You're told when you are really small not to talk to strangers, but it only really scratches the surface," says Tim, now 20. "No one says this is what will happen or tells you what it is like to be caught up in it."
There is no doubt that it is an unpleasant subject, and one that teachers would not be alone in wanting to avoid. But if more children are not to follow in Emma and Tim's footsteps, it is a nettle that has to be grasped.
* Some names have been changed. With the exception of the Derby case, all photographs are posed by models and used for illustrative purposes only.
Abid Saddique and Mohammed Liaqat were jailed earlier this year after being found guilty of sexual offences against children. The pair were part of a gang who cruised around places in Derby where children congregate, such as schools, parks and shopping centres, in search of victims. Gang members were caught on CCTV luring girls to their car.
Indicators of possible sexual exploitation
Disengagement with education or significant change in performance at school
Volatile behaviour exhibiting mood swings or abusive language
Change in appearance
Acquisition of expensive clothes, mobile phones or other possessions without plausible explanation
Evidence of drug, alcohol or substance abuse
Low self-esteem, self-harming behaviour, eating disorders or promiscuity.
Original headline: `One girl is madly in love with one of the men and wants to have his baby'