While the stunt took place more than two years ago, its effects coincided with satellites taking photographs of Hamilton for Google Earth, meaning web users cop an eyeful whenever they view Fairfield College.
Local resident David McQuoid told the Waikato Times he was online searching for a property when he came across the crude etchings, some of which measure almost 15 metres (50 feet) long.
"At first I thought it was a large piece of art work," he told the newspaper.
The school's acting principal Gerhard van Dyk was less convinced of the symbols' artistic merit, telling the Times he had been unable to catch the pranksters, who burned the phalluses into the grass on a weekend in May 2009.
By the time he arrived at the school the next Monday, the grass was already dying and giant penises were emerging all over the property.
A total of six became apparent in subsequent days, as school authorities scrambled to cover them up.
"There's not really much we could do about it," he said. "The caretaker took some more weedkiller and tried to camouflage it a bit."
Van Dyk said he would contact Google about removing the etchings but the Internet giant told the Times that they could not be blurred, as Google Earth images came directly from satellites, unlike those used for Google Street View.
Online reaction to the stunt on Fairfax Media's stuff.co.nz website was mostly positive, with one reader commenting: "A funny harmless prank, much better than the kids robbing houses or burning down buildings."
However, there was some outrage, including a reader who posted: "This is not funny, what a sick sense of humour you people have... This shows the twisted minds of today's youth."