Children as young as 12 are coming to school under the influence of a 'legal high' drug linked to deaths and serious illnesses, teachers have revealed.
Pupils are turning up to lessons disorientated or suffering physical symptoms such as nose bleeds after taking 'meow meow' - a drug sold legally as a fertiliser over the internet.
Others are disrupting classes after snorting it on the bus to school or taking it during lunch breaks.
The revelation came as a teenage boy died at a house party this week after experimenting for the first time with the drug.
The body of Ben Walters, 18, was found sprawled beside a 28-year-old woman who is now fighting for her life in hospital.
Both are understood to have taken 'meow meow', which is formally known as mephedrone and can be bought for as little as £4 a gram.
Teenagers are now being given emergency warnings about the dangers of a drug linked to the death of 14-year-old Gabrielle Price in Worthing last November.
A 17-year-old sixth-former collapsed at Woldgate College, in Pocklington, near York earlier this month after apparently taking a dose outside school during his lunchbreak.
Pupils and teachers watched in horror as he became seriously ill and had to be rushed to hospital suffering from an irregular heart-beat, chest pains and breathing problems.
Jeff Bower, the college's head teacher, said the drug should be made illegal immediately.
'You can't think anything else after seeing that young man struggling like that - it scared the life out of everyone here,' he told the Times Educational Supplement.
'We are not extremely receptive to this problem - it's been a big wake-up call.
'It was the first time he had taken it and he admits it was because of peer pressure.
'This has just hit us completely between the eyes.
'We held a special assembly about the situation and built it into our drugs education programme.'
Mephedrone - also called 'drone' or 'bubble' - was first used on the club scene in 2007 and comes in powder, tablet, crystal or liquid form.
It is legal providing it is not processed or marketed for human consumption.
Its effects are similar to ecstasy and cocaine. Users can display symptoms such as nose bleeds, headaches, rapid heartbeat and a purple discolouration of the skin, which can last for several weeks.
In Harrogate, police said teachers had noticed 'a very rapid physical and mental decline in pupils using legal high drugs - and some just aren't there any more'.
Sergeant Geoff Crocker, safer neighbourhoods officer for Harrogate, said: 'It's easily available and cheap and we've seen enterprising pupils start selling it in school.
'One young girl we know is addicted to mephedrone and she is active sexually with a number of men for money to pay for it.
'I know our schools are concerned about this, and are working hard to deal with it.'
In County Durham, five people were hospitalised last November after taking the drug.
Teachers have reported it causing disruptive behaviour among students.
Darren Archer, manager of the County Durham drugs and alcohol action team, said: 'We've mostly seen it used as part of a risk-taking culture among young people, particularly in colleges.
'We've had anecdotal reports of it causing bad behaviour and now we are trying to offer comprehensive support to teachers and children.'
Meanwhile in Brighton some pupils have been spotted taking the drug on the school bus.
Police officers are to talk to youngsters about the dangers of legal highs in personal, social and health education (PSHE) lessons.
Sam Beal, acting healthy schools team leader for Brighton and Hove City Council, said: 'It's clear that increased numbers of 14 and 15-year-olds started using meow meow at the end of last summer and we have big concerns about this.
'Teachers hear about this more and more and they are concerned that the drugs are being brought into schools.'
The death of Ben Walters at a house party in Berkhamsted, Hertfordshire was the latest tragedy to be linked to the drug.
He was studying drama at Amersham and Wycombe College and hoped to go Leeds University to do a media studies course.
Torri Ivers, 16, a college friend of Ben's, warned the public needed to be told about the dangers of mephedrone.
'Nobody thinks it's dangerous because it's legal. It's a substitute for heroin but you can get it over the internet,' she said.
'You can buy it in college because it's cheap and nobody realises how bad it is until something happens. Nobody has been taught enough about them.
'It was the first time Ben had ever taken drugs. He had a lot going for him and got good grades.
'I can't emphasise enough how much of a lovely, beautiful person he was. It's not fair.'
The Advisory Council on the Misuse of Drugs is currently researching mephedrone's effects and is expected to advise ministers to make it illegal under the Misuse of Drugs Act.
January 22, 2010
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Legal but lethal: The drug snorted by school kids which is sweeping Britain