Animal activists are calling for wider discussion about killing possums, saying current methods are cruel.
Drury School in South Auckland has come under fire from the SPCA after it drowned possum joeys in a bucket during an annual fundraising possum hunt.
The semi-rural school takes part in a fundraising possum hunt and this year some hunters, who were required to have firearm licenses, failed to remove and humanely dispose of joeys.
The school said no students were involved in the killing.
But SAFE chief executive Jasmijn de Boo said allowing children to be part of an event that killed animals sent harmful messages.
She said the country needed to reconsider how it dealt with possums.
"We cannot be using these methods, certainly not drowning, but even 1080 poisoning and traps are very cruel."
A more humane approach was needed, she said.
A professor of veterinary neurophysiology at Massey University, Craig Johnson, said the most humane method of killing a joey depended on its stage of development.
Dr Johnson said if the joey foetus was younger than 120 days, then leaving it to die was acceptable.
"If you happened to kill a pregnant mammal with a foetus still undeveloped the evidence says the animals don't achieve awareness so there wouldn't be a welfare issue."
He recommended using a gun if the joey was older.
"Joeys that are putting their head out of the pouch and looking around and climbing in and out of the pouch really need the same degree of care in killing them that you would take with a pet animal or farm animal."
If there was no gun available, he recommended blunt force but if that was carried out poorly, it could cause the animal to suffer.
If a person lacked confidence in killing an animal then it was best to avoid the situation, he said.
He said a document on the methods of killing animals by the American Veterinary Medical Association, which the Animal Welfare Act cites, was considered the best guide.
Dr Johnson said drowning animals was never recommended as a humane technique as it would cause the animal considerable distress.
People had to model good practice to others that were witnessing the way the animals were treated, he said.