The survey showed more than 20 respondents claimed they had been raped.
The survey was sent to 1042 pupils and 725 participated - a response rate of 71.2 percent.
School principal Christine O'Neill said police were at the school on Tuesday, speaking with each year group at their assemblies.
"Three girls came forward yesterday to formally report incidents and nine have spoken with police and our counsellors, and are considering more formal reporting.
"They are being well supported. The safety and wellbeing of our staff and students remain our number one priorities A number of students went home yesterday after the morning assembly at which we told them about the survey.
"There's no doubt the information was triggering for some students."
O'Neill said the feedback from pupils after the release of the survey was "we are not alone".
"It was this that brought a number of them forward to report their experiences."
More than a quarter of survey respondents said they had been sexually harassed more than 10 times - and more than 20 said they had been raped.
Detective Inspector Greg Murton, who is assisting the school, said he expected more girls to come forward.
"We often see this. As one feels they can come forward, others do too. That's why shining a light on this unacceptable behaviour and supporting people to report it, is so important."
O'Neill said she hoped the wider conversation that has resulted around the country continued.
"The kōrero now must happen between ministers, schools, community support agencies and the Education Review Office (ERO).
"As our head girl, Amiria Tikao, said so eloquently yesterday, we have lit the fuse; it must not be allowed to go out."
