Twenty-five classmates picked up enough rubbish to fill several bags provided by the Sustainable Coastlines Trust.
"Beaches are dirty because some people have beach parties and they leave their rubbish around when they should take it home," said Brandi Danny, who found glass, plastic wrappers and rags.
"I was surprised that Waiheke has heaps of rubbish in the sand."
A class from another decile one school - Manurewa South Primary - joined in for the Love Your Coast day trip to Waiheke, which continues with other South Auckland schools and culminates in a clean-up by volunteers using boats and kayaks at the weekend.
Assistant principal Karen Hohaia-Turuwhenua said being on a ferry was a new experience for some of the children.
"On previous years' trips, some students have not only never been on a boat but also have never been to a beach. That was an eye-opener for the students.
"We have a big thing going on at our school about keeping it clean and we have our litter wardens.
"This trip is about raising awareness of how rubbish is going into the sea and when the children get older they will help look after New Zealand."
Trust chief executive Sam Judd said 96 per cent of those who had heard a trust presentation said they would talk to other children at their school about littering and encourage them to buy plastic products that could be recycled.
Love Your Coast
991,384 litres of rubbish picked up by volunteers since 2008
95,139 educational talks by Sustainable Coastlines Trust
33,392 people took part in the Hauraki Gulf clean- ups