Hundreds of children in England, some as young as five, have been excluded from school for sexual misconduct including watching pornography and sharing indecent images, an investigation has found.
There were 754 reported incidents between July 2013 and April 2017, including 40 of children below 10.
But the true figure is thought to be much higher as the majority of councils contacted for the investigation said they did not hold the information or refused to disclose it.
There were seven cases of children in the first year of school being involved in sexual misconduct and for every incident involving a girl, there were 18 that involved boys, the data released by local authorities in England showed.
There was a surge in incidents as children reached secondary school - with 66 cases involving 12-year-olds, peaking at 120 for 14-year-olds - the most likely age group to be involved in sexual misconduct.
The data has prompted calls for sex education to be "dragged into the 21st century".
An NSPCC spokesman said: "Social media, sexting, online porn and dating apps did not exist when sex education was introduced on the curriculum a generation ago.
"It must be dragged into the 21st century, it must be consistent, and it must be offered in every school as part of a broader PSHE (personal, social, health and economic education) curriculum."
In March, the Government announced children would be taught about healthy relationships from the age of four, with sex education compulsory in all secondary schools, from September 2019.
Sarah Green, co-director of the End Violence Against Women Coalition, said: "These figures, which reveal really alarming behaviour in schools, show that girls and boys are being failed by those who should protect them and prevent this.
"The Department for Education (DfE), and school leaders and parents, need to take responsibility now for ensuring better child protection, better policies on bullying which recognise sexual bullying, and good relationships and sex education. We can change this."
The data was based on results from 15 local authorities with data.
A DfE spokesman said: ""As announced in March 2017, all primary schools will be required to teach relationships education and all secondary schools will have to teach relationships and sex education in the future."
Figures released last month by the Government show there were 2,070 fixed-period exclusions for sexual misconduct in English schools for the academic year 2015/16, as well as 70 permanent exclusions for the same reason.
The data was collated from all state-funded primary and secondary schools, as well as special schools, but did not specify the age of children involved.