Police have become involved after reports schoolmates of a Down syndrome girl posted videos online of her flashing her breasts and licking the ground.
The Wellington East Girl's College student, 15, was bullied by a group of girls who pretended to be her friend then encouraged her to do the demeaning acts, Fairfax reported.
The group shared footage of the girl on Facebook and Snapchat, captioning it with "slag" and "yummy".
Principal Sally Haughton sent an email to parents saying the school had been working with police from early on, Fairfax reported.
"We are involved in an investigation related to the taking and circulation of images of a Wellington East Girls' College student on social media," her email said.
"I cannot discuss the details of the investigation for privacy reasons. We have taken this situation very seriously and have been working with the police from the early stages."
She said the school had "processes to support investigation that are robust and fair".
Police would not comment on the case, but a spokesperson said bullying could cause serious harm to victims and where necessary, further action may be taken by police.
"We encourage young people to talk to a trusted adult, such as a parent or a teacher, or to talk to Netsafe.
"Under The Harmful Digital Communications Act, Netsafe offers a free service for people in New Zealand to help with online bullying, harassment and abuse - it is available seven days a week on 0508 NETSAFE (0508 638 723).
"As a precautionary measure, police encourage young people to ensure they are cautious about personal details provided online and regularly change their passwords.
"Most social networking sites including blocking and unfriending people and reporting content. Additionally, phone numbers can be blocked on your phone where necessary."