Many 13-year-olds have sent photographs of themselves naked or performing sex acts by text to classmates, experts said today.
Parents are being warned to monitor their child's mobile phone use as they may be 'sexting' regularly.
Research has found teenage boys often send photographs of their genitals to female pupils, while young girls reciprocate by sending naked pictures of themselves carrying out sex acts, or with their boyfriend's name scrawled on their breasts.
Some pupils are so pressured to send sexual photos they trawl the internet looking at child porn to find suitable images they can send, one teacher has said.
'I’ve had pictures sent to me of boys’ private parts who I don’t even know. They want you to send one back,' one anonymous 14-year-old girl from Southampton said today.
'A lot of boys I know watch porn all the time so maybe it’s why. It might shock parents but it is just normal at schools. It happens all the time but then everyone has a phone.'
Another girl said: 'We had a case in my school where a naked picture of a girl from another school was being texted around and everyone saw it.'
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A school survey has been carried out by Michelle Barry, who works with 7,000 youngsters aged seven and above as part of the Southampton Rape Crisis' preventative education STAR project.
On one occasion a class of 13-year-olds was asked to raise their hands if they had sent an explicit naked picture of themselves and every child put their hand up.
Dangerous: Some youngsters are trawling the net for child porn images as they feel pressure to send them, one teacher said
'I was gobsmacked', Ms Barry said, adding: 'What is most worrying is the fact young people do not identify this as a problem. For them it is part and parcel of school life.
'Sexting is a huge issue and something we are hearing about more and more. Sharing pornographic images is common place.
'If the only sex education these children get is from watching pornography, that causes huge problems around things like body image and, more scarily, surrounding issues of consent, contraception and relationships.
'Pornography can be hardcore, violent and extreme. There are some horrific sexual practices they think are the norm now. If young people become immune to that when they are thinking about having sex for the first time, they might want to emulate what they have seen – that’s a scary reality which we are faced with today.'
Warnings: Parents should try to be more aware of what is being sent from their child's phone, experts say
Ms Barry conducted the survey among Year 9 pupils and found the average child is first exposed to pornography aged 11.
It has led to more concern about the negative impact of sexual material on Britain's children.
Jon Brown, sexual abuse leader at the NSPCC, said: 'The regular and normalised consumption of hardcore pornography among young people has contributed to the explicit sharing of self-generated imagery.'
Last week it was revealed teachers have been encouraged to introduce pornography into the classroom, using sex education lessons to explain that porn is 'not all bad' and 'hugely diverse'.
The recommendations, included in an educational guide, suggest that teachers confront 'myths' about porn and inform children as young as five about sexualisation.
The guidance could have significant influence in British schools after the Government's decision to keep sex education lessons voluntary, leaving schools to devise their own ways of teaching the subject.
The Daily Mail has led a long-running campaign to introduce measures to protect young people from the growing influence of porn.
But the guidance, produced by a coalition of charities, encourages dialogue in the classroom about all aspects of pornography.
Issued by the Sex Education Forum, whose members include the NSPCC and Barnardo's, the guidance encourages teachers to inform children over the age of 11 about subjects such as sexting, whereby sexually explicit images and pictures are sent in text messages.
Critics said that parents would be 'horrified' by the possible introduction of pornography into classroom lessons.