Updated 5.05pm: An Auckland school has banned an anonymous messaging app, over fears it's a breeding ground for cyber bullying.

Diocesan School For Girls blocked the app Yik Yak on school grounds, after students came to staff, reporting that nasty comments were being posted.

Principal Heather McRae says the school tries to ensure its students have the same values in the physical world as they do online.

"So their behaviours are the same, their beliefs are the same, and that's something we feel quite passionate about."

Heather McRae says a group of year 13 pupils came to staff, concerned about negative comments being made about other students.

She says the school is really proud the girls recognised the app's dangers for themselves.

"We've been trying to build digital citizens with important values and responsibilities, and it's great to see that coming through.'

Heather McRae says when it comes to cyber bullying, the school wants its students to be 'upstanders', not bystanders.