It may have been back in December 2006, but Lisa Goodman still remembers the incident as if it were yesterday. “I was walking my dogs quite late one night after being out and I found a girl who was beyond drunk, lying face down in a river near my house,” Ms Goodman recalls. “I saw that it was one of my students from school - I had a lot of interaction with her and her older sister. She would have been about 14 at the time.”

Ms Goodman called an ambulance and the girl was taken to hospital. “Initially, you go into autopilot when you come across that situation, but after that, for me, it was devastating,” says Ms Goodman, a pupil support manager at Deans Community High School in Livingston, West Lothian. “I spent the whole weekend thinking: Is she alive? Is she dead? It was horrible. I’m a parent as well, and I kept thinking about her mum and dad. She was left on her own, abandoned. It was really scary stuff.”

Unfortunately, this is an increasingly familiar picture on a Friday evening: pupils drinking to excess, followed by a trip to accident and emergency. If they’re lucky, they may have a friend to accompany them on the way, but often they are alone when they are picked up by the emergency services.

Just under a fifth of 11 to 15 year olds in England have had at least one alcoholic drink in the last week, according to Department of Health figures. Last month, a nine-year-old boy in Brighton was found to be suffering from alcohol dependency after council officials investigated his family’s anti-social behaviour.

When it came to drugs, 15 per cent of 11 to 15 year olds in the South West had taken drugs at least once in the previous year, rising to 20 per cent in the North West. Cannabis was the drug of choice.

But while young people rarely bring alcohol or drugs into school, pupils’ social habits at the weekends or evenings can have a stark impact on their behaviour and concentration in the classroom.

At Deans Community High, teachers tell Ms Goodman when they are worried about a pupil in their class. “You get young people coming into school hung-over,” she says. “The youngest we’ve had was probably 13. They might be very sleepy in class, or very listless. I’ll go and speak to them and they will tell me they were drinking last night, or the night before, and they’ve got a raging hangover.”

Patterns start to emerge among pupils who are regularly drinking or taking drugs, says Brian Lightman, general secretary of the Association of School and College Leaders (ASCL) and former headteacher of St Cyres School, in the Vale of Glamorgan. “We know that there are children who come in at the beginning of the week and you can tell they’ve been out at the weekend and they’ve been drinking,” he says. “They’re tired, they haven’t had enough sleep, and they’re not in the right frame of mind to work.”

In Mr Lightman’s experience, the signs are only visible with a minority of pupils who are experimenting with alcohol and drugs. But all the same, “it is something that you have to be mindful of,” he says. “If children are involved in drugs, you begin to see the effects pretty quickly. With cannabis, it is mood swings. Teenagers can be pretty moody anyway, but this is quite extreme - they can be disruptive and then disengaged.”

When it comes to alcohol and drugs such as cannabis, the effects can be subtle. But when Class A drugs such as ecstasy are taken, the results are often dramatic.

Now 19, Sam* smoked his first joint at the 13, “probably before I had my first drink”. At that age, the local dealers would not sell to him, but as he got older, smoking cannabis, taking mephedrone (meow meow) and drinking became part of life.

“I didn’t usually smoke weed (cannabis) at school, but I got really stoned one lunchtime,” says Sam. “I was completely baked, but we had history class with a really strict teacher later on that afternoon. I put up my hand to answer a question and then forgot what I was going to say.”

This happened a few times before one of his classmates asked if he had been smoking cannabis. “I said `yes’, and the teacher heard and sent me to the headteacher’s office. I told them I was just joking, but after a long discussion I was sent to the nurse. I said I was just really tired and talked to her for a while and, thankfully, she cleared me.”

It is not just the day-to-day disruption, however, but the long-term effects on pupils that are of concern. Studies have shown that pupils who drink frequently are three times more likely to fall behind with their school work than their peers and are more likely to play truant. “You can actually see their academic achievement, their enthusiasm, their motivation for school deteriorate,” says Ms Goodman. “If you plotted it on a graph, you would see that deterioration.”

Smoking cannabis made studying much more difficult, agrees Sam. “It definitely makes you much less driven,” he says. “I did nine pieces of art for my A-level throughout the whole year, then I had to do it all in the last two weeks to try and catch up.” The first couple of times Sam took ecstasy, the impact was worse and lasted longer. “I was definitely still feeling the effects a week later,” he says.

However, much as with adult drinkers, there are pupils who binge-drink or take drugs and do very well at school. Studies have also shown that the drinking habits of young people from supposedly “middle-class” backgrounds can be just as shocking as those from poorer ones.

Academic results at Sam’s school were high, and the school prided itself on its reputation. And yet heavy weekend drinking and mephedrone parties were the norm. By the time they got to sixth form, a minority of pupils were taking drugs regularly, sometimes in school during afternoon-free periods.

“I think a lot of people who drink or do drugs are determined and have quite high levels of stress,” says Sam. “One girl I knew was a massive pill-head and was always out drinking. But she got 10 A-stars at GCSE and four As at A-level. She’s off to Cambridge. It is necessary for a lot of people to relieve stress.”

Ms Goodman didn’t realise that underage drinking was such a widespread problem among young people until she started working at Deans Community High. “I’m not a teacher so kids tell you stuff all the time,” she says. After seeing her 14-year-old pupil suffering from hypothermia and coming so close to death, she decided to take action.

Two months after the incident, Ms Goodman arranged an interdisciplinary meeting between the school, the police and health service to try to tackle underage drinking in the area, and Operation Floorwalk was established.

Every second Friday, as soon as school finishes, small teams of community police officers plus Ms Goodman, are despatched to known drinking spots in Livingston and surrounding towns. Anyone under the age of 16 in possession of alcohol is brought back to the police station where drug and alcohol counsellors are on hand to give advice and arrange follow-up care with parents if necessary.

Crucially, Ms Goodman calls the school of each pupil to tell them they’ve been picked up. “It is not as a punishment - it is genuinely about intervention,” she says. There has been a marked improvement in pupils’ behaviour following Operation Floorwalk. Between September 2007 and August 2008, police reported a 38 per cent reduction in the number of phone calls complaining about anti-social behaviour.

Community-based partnerships are becoming increasingly common. At one of his previous schools, David Shaw, vice-principal of Grace Academy Darlaston, in the West Midlands, worked closely with the local housing association, which alerted the school to a group of 13 to 15 year olds who were drinking on the streets on Friday and Saturday nights.

“It was like a mini booze cruise for them, not with pubs, but they had stop-off points on a route through the estate, where they’d get cigarettes and alcohol,” says Mr Shaw. The group did not take substances into school, but it affected their attitudes in class. “They would be apathetic,” he says. “They’re there in body but not in mind, not really knowing what’s going on.”

One of the boys in the underage drinking group had a mother who was an alcoholic and he would swing between abstinence and binge-drinking. “We put a learning mentor in place to work with him and look at the dangers and consequences of what he was doing,” says Mr Shaw. “He completely understood, as he knew what it had done to his mum and his family. But it was almost instinctive for him to do it. It was such a challenge for him not to do that, even at 14.”

The national charity Alcohol Concern would like to see a more preventative approach to underage drinking that focuses on young people’s health and well-being. “Young people’s drinking has been very much viewed through the lens of the public prosecution service and not so much viewed in a public health context,” says its youth policy adviser, Tom Smith. “For example, looking at the effect it would have on young people’s health. I think there are more robust routes to access support for young people within the criminal justice system.”

The agency is assessing the information, support and advice available for young people suffering from alcohol or drug abuse, particularly when they are treated in hospital. At the moment, there is no way of knowing whether young people are being repeatedly hospitalised and there is no after-care and support, says Mr Smith. “Effectively, people are patched up and sent on their way,” he says. “Young people could be reappearing at Aamp;E, and we wouldn’t know.”

Most information about alcohol and drugs use focuses on the element of risk-taking, says Boo Spurgeon, head of PSHE at Wisewood School and Community Sports College in Sheffield. Course content presupposes that teenagers will drink, as anything else will seem unrealistic and irrelevant to pupils. “Alcohol is seen as intrinsic, and this is something that we try and tackle in PSHE,” says Ms Spurgeon. “But it is very difficult to separate out the notion that having a good time doesn’t necessarily have to involve alcohol. They don’t believe you.”

Children should be educated on how to make an informed choice, says Ms Spurgeon. “I certainly tend to take the approach of if you are going to drink, then you need to know how to drink safely so you don’t put yourself at risk and make stupid choices,” she explains.

The impact of underage drug-taking tends to be less obvious to the public eye than binge-drinking. When the deaths of two teenagers in March last year were linked to mephedrone (incorrectly, as toxicology reports later found), the huge popularity of this then-legal high among young people was finally brought to light.

But unlike binge-drinking, most teenagers are more covert about their drug-taking habits. When it comes to alcohol, the vast majority of young people are influenced not just by their peers, but by their parents and other adults. For Annetta Minard, headteacher of Oakmead Technology College, Bournemouth, the biggest problem is that drinking to excess is accepted as the norm.

“They are all exposed to alcohol but it might be in different contexts,” says Dr Minard. “Many of our parents spend a lot of time in the pub and will drink at home. For other middle-class households, I imagine it would be more through dinner parties, or by parents drinking wine every night.” As a result, it can be difficult to demonstrate to pupils the difference between socially acceptable drinking and drinking to excess.

It is also hard to communicate the dangers of underage binge-drinking in a culture that celebrates alcohol. “Young people are under enormous pressure, from the media and from the fashion industry, to start drinking from the time they are teenagers,” says ASCL’s Mr Lightman, and for many teenagers, the same is true of drugs.

Faced with these formidable obstacles, the best teachers can do is take a “harm minimisation approach”, advises Ms Spurgeon. Educate pupils about the risks and the consequences of alcohol and drug abuse and, hopefully, fewer will end up face down in a ditch, or worse

*Name has been changed at student’s request.