Children as young as five have been excluded from schools for serious sexual abuse, watching pornography and sharing inappropriate images of themselves.
Records obtained by the Press Association show hundreds of pupils have been banned from class for a raft of "sexual misconduct", including assault, harassment and bullying. Others have been excluded for inappropriate touching, lewd behaviour and sexual graffiti.
Some children were disciplined within their first year at school - when new learners are aged between four and five - while 13, 14 and 15-year-olds are the most likely to be sanctioned.
The investigation found there were more than 2,000 reported incidents between January 2010 and September 2013. However the true figure is likely to be much higher, as nearly two-thirds of the 153 authorities contacted said they did not hold the information centrally, or refused to disclose it.
Child welfare charities and politicians described the figures as "extremely concerning" and called on the Government to clamp down on the ease with which children can access internet pornography, and to implement a "robust" sex education programme.
Jon Brown, head of tackling child sexual abuse at the NSPCC, said: "The extent of sexual harassment, inappropriate sexual behaviour and in the worst cases violence by children is extremely concerning.
"Exposure to extreme, sometimes sexually violent and degrading material is now only a few clicks away and this can warp young people's views of what is normal and acceptable sexual behaviour. Sexting (sending sexual text messages) is now the norm for many young people who may find once they start sending explicit pictures of themselves the situation spirals out of control.
"We need good quality, age appropriate education in schools to help young people develop healthy, positive relationships with each other, so that children understand consent, do not feel so pressurised to behave in a sexualised way, and respect themselves and others."
Six children in reception classes across England were involved in a sexual act in a school, the figures showed. There were a further 15 incidents involving six and seven-year-olds, rising to 69 incidents for children in Year Six (age 11) at the time of the sexual misconduct.
There was a surge in incidents as children reached secondary school - with 175 incidents in Year 7. The figures show further increases in the next three year groups - with 248 incidents for 13-year-olds, 256 for those a year older, and 240 for those in Year 10 (age 15).
Former children's television presenter and Lib Dem peer, Baroness Floella Benjamin, said she was not surprised by the data, having heard anecdotal evidence and received reports from charities of incidents involving very young children.
She said: "I believe one of the main contributory factors is children being exposed to pornographic online material which is easily available on the internet, and they are emulating what they see. They want to discover what it feels like to experience the sexual act they have seen and if they don't achieve the level of satisfaction they expect they move on to the next girl.
"We need to have a robust sex and relationship education programme rolled out across all schools in the country for children and young people, which is age appropriate, to help them understand the true meaning of love, respect and unconditional sexual relationships."
The former Play School presenter said young boys are "becoming addicted to pornography" and that teachers needed training to detect changes in children's behaviour patterns which might hint at their involvement in abuse.
She added: "We have to teach them that sex is about mutual respect."
The large majority of incidents concerned boys, with only 9% involving girls.
However, there were some gender spikes in the data. A spokesman for the London Borough of Hillingdon said: "The most concerning issues involve so-called 'sexting' with children communicating inappropriately with each other through mobile technology.
"There are also occasional reports of under age sexual intercourse, which do not reach the threshold for a criminal investigation, though the police are informed about such incidents. Also sexualised behaviour, such as masturbation is a common theme.
"In terms of the overall picture including informal consultations as well as formal referrals, the majority are females (55%)."
Many authorities said incidents of sexual misconduct appeared to be decreasing.
A spokesman for Derbyshire County Council, which was among those to see a year-on-year decrease in reported incidents, said: "We support schools with their work to prevent incidents, and to learn from any that happen so they can safeguard against them.
"Our on-going work to reduce the number of fixed-term exclusions includes measures to prevent and deal effectively with any problems of this nature.
"We also run our anti-bullying 'Stop!' campaign with schools, and restorative justice programmes so students understand the consequences of their actions."
A Department for Education spokesman said: "We share headteachers' serious concerns over sexual misconduct by pupils. That is why we have given teachers the power to search for and delete inappropriate images from phones, while the Child Exploitation and Online Protection Agency and the Sex Education Forum have produced useful material to help schools deal with 'sexting'.
"Schools should teach pupils about respect for others and how the law applies to sexual relationships. And our statutory guidance is crystal clear - if a professional thinks a child is at risk of harm they should report it immediately to social care.
"It is encouraging that official statistics show exclusions for sexual misconduct are decreasing year on year and represent less than 0.05 per cent of exclusions across the country."
The figures come after a damning report last month by the Office of the Children's Commissioner for England, which warned that youngsters across the country are being exploited and that the authorities responsible for their safety are failing to protect them.
The two-year inquiry found that 2,409 youngsters were known to be victims of child sexual exploitation by gangs and groups, while a further 16,500 were at risk.
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