Lincolnshire Police classed 36 alleged incidents as sexual offences in the county’s schools in the four years between 2011/12 and 2014/15.
There were four reports of sexual offences on school premises recorded in 2011/12, seven in 2012/13, 18 in 2013/14 and seven in 2014/15.
Reported offences included rape, sexual assault, exposure and voyeurism, abuse of position of trust of a sexual nature and sexual activity involving a child.
Plan International UK is calling for the government to commit to mandatory sex education which covers sexting, consent, healthy relationships and the law.
Plan International UK Head of Girls’ Rights, Kerry Smith, said: “This shows that we’re failing young people when it comes to learning about healthy relationships and consent.
“Quality sex and relationships education helps young people to develop healthy attitudes towards sex and relationships while helping to tackle inappropriate and aggressive sexual behaviour.”
Figures were disclosed after a Freedom of Information request of UK police forces with 34 of 45 responses across England, Wales and Northern Ireland. Police Scotland declined the request on cost grounds.
Alleged offences ranged from harassment to serious sexual assaults and rapes. Less than one in 10 suspected cases resulted in criminal charges or summons.
Ms Smith added: “Clearly girls and women are disproportionately affected by sexual violence in schools.
“Young people need education about the realities of life and relationships, including consent.
“This is a global problem. Girls and boys need clear messages that unwanted sexual contact in or around school is not acceptable.”
Earlier this year, Plan International UK revealed how one in five women in the UK had experienced sexual violence in or around school as schoolgirls.
Plan International UK works with children and their communities in more than 50 countries worldwide.