The biggest problem facing teenage schoolgirls is the pressure to start having sex, according to a survey by global children's charity Plan UK.
Chief executive Tanya Barron said: "Pressure to have sex can have a disastrous impact on young girls in the UK and around the world – damaging their health, wellbeing and education.
"Our international report shows that sexual violence in particular disproportionately affects girls around the globe – especially in and around school."
As part of Plan's global Because I am a Girl campaign, it has estimated 150 million girls and 73 million boys have experienced sexual violence around the world. And nearly half of all sexual assaults worldwide are committed against girls who are under 16.
Plan UK is calling on the Government to lead global action to end gender-based violence in and around schools.
The charity is also asking ministers to replicate successful projects and to invest in research to increase the impact of their work.
Ms Barron added: "Taking steps to prevent violence in and around schools enables girls and boys to complete a quality education, and it can help prevent attacks in later life by challenging behaviour early on."