A gang of teenage girls urged a 15-year-old special needs student to flash her breasts and then filmed and shared the footage online.
The Wellington East Girls' College students pretended to befriend their schoolmate Holly Reed, who has Down syndrome, and encouraged her to perform tasks like licking the ground, reported Fairfax.
They then reportedly shared the footage on Snapchat and Facebook with captions such as "slag" and "yummy".
It breaks your heart seeing things like that
The images were shared among students for months before the school and her parents found out.
"It breaks your heart seeing things like that," Holly's father Michael Reed told Fairfax.
The bullying was only detected after other students reported the images to the school.
Mother Nicki Crawford told Fairfax it had gone on over a period of months, and Holly had not been aware of what the girls were asking her to do.
Holly said she was saddened by what happened. "They were my friends," she told Fairfax. "I would like them to say sorry."
She didn't want them to do the same thing to anyone else, she said.
A meeting had been held with the school and some of the students, Reed said, but laimed only one student admitted they'd done anything wrong.
"The attitude of the girls was that: 'We're just teenagers, it's the dumb s... that we do'."
Principal Sally Haughton told Fairfax the school was taking the incident very seriously. It had been working on the situation for the past week, she said, but were not yet sure how many students had been involved.
"Our deputy principals and our guidance teams have been working very hard to make sense of what's occurred and the information that's available to us."
At the meeting with families and students, there were some apologies made, she said.