Amanda Spielman made the comments after a damning investigation found sexual harassment had become so normal in schools that children no longer see the point of reporting it.
The review found easy access to pornography has set unhealthy expectations of sexual relationships and schoolboys share nude photographs of girls “like a collection game.”
However, Ms Spielman stressed it was part of a “wider social problem” that schools cannot solve alone.
She told ITV’s Good Morning Britain: “Teachers and leaders we spoke to often underestimated the scale of problem.
“Sometimes they didn’t see it as a problem, but more often they were simply not aware of the extent to which it was happening.”
Ms Spielman added: “It’s absolutely not just a schools problem. It’s a wider social problem.”
She said there were issues for Government and suggested they had an opportunity to consider how to carry forward Ofsted’s recommendations with their Online Harms Bill.
As part of the review, inspectors visited 32 state and private schools and colleges and spoke to more than 900 children about sexual harassment.
They found nine out of ten girls said that sexist name-calling and being sent unwanted explicit pictures or videos happened “a lot” or “sometimes.”
Boys talk about whose “nudes” they have and share them on platforms like WhatsApp or Snapchat, they said.
In one school girls said some pupils can be contacted by up to 11 different boys a night asking for nude pictures.
Some evidence suggests inappropriate images and videos are being shared in primary schools.
Meanwhile, some girls experience unwanted touching in school corridors.
The Ofsted report called for a culture change in schools and colleges, with headteachers assuming that sexual harassment is affecting their pupils even when there are no specific reports, and for more time spent teaching children about consent and sharing explicit images.
The Department for Education said that in response to the review, there will be more guidance on sex education and schools will be encouraged to dedicate staff training days to handling sexual abuse and harassment.
Education Secretary Gavin Williamson said: “Sexual abuse in any form is completely unacceptable. No young person should feel that this is a normal part of their daily lives – schools are places of safety, not harmful behaviours that are tolerated instead of tackled.”
Mr Williamson asked Ofsted to launch the rapid review of sexual harassment in schools following the Everyone’s Invited scandal, in which thousands of anonymous testimonials of abuse were published on the website.