However, an email from EGGS principal Madeline Gunn to parents this week appeared to hint that might not always be the case.
"At this stage it's proposed these areas will become shared zones and students will have the right to attend the school of their choice," wrote Ms Gunn. "However, if this right continues in the future when pressure may increase on the EGGS roll, is not clear.
"The board has made no changes to the present EGGS zone for the next three years."
Adrien de Croy, who lives with his family in a home zoned for EGGS and also within the proposed One Tree Hill College zone, understood there was significant pressure on the rolls at AGS and EGGS.
"They can't really reduce the zones unless there's an alternative in place, and [the proposed One Tree Hill College zone] basically gives them the opportunity to reduce their zone. We see it as the first step to removing us from the Auckland Grammar and EGGS zones."
Mr de Croy, whose eldest child is 7, said at this stage his main concern was for the value of their property. A real estate agent had told him a typical premium someone would pay to get into the "double Grammar zone" was about 20 per cent.
Last year the Herald reported one Mt Eden home just 750m outside the area went for $516,000 less than a house up the road, valued the same but situated 250m within the zone.
One Tree Hill College principal Nick Coughlan said he understood such concerns, but they were unfounded.
The zone, and any overlaps, was informed by the need to not divide areas and homes around contributing schools. There was no intention to realign zones in the future, Mr Coughlan said.
The college's roll had shot up from 700 to 1000 in five years, and that reflected the good news that the community now wanted their children to attend.
Doug Crutch, who has a daughter at EGGS and would be in the shared zone, said other Auckland schools had shared zones for years and stopping the proposed zone wouldn't necessarily stop future changes.
Ms Gunn said the EGGS board was to meet the ministry last night, and there was no intent to change the school's zone in the future.
"We just felt that those people living in those areas should be made aware of [the proposed zone]. They don't know, and we don't know, what it might mean in the future."
Katrina Casey, the ministry's head of sector enablement and support, said the proposed zone also overlapped with zones for Onehunga High School, Selwyn College, Otahuhu College, Edgewater College and Glendowie College.
There was no proposal to reduce the existing home zones of affected schools. The only reason to change a shared zone would be to avoid overcrowding, Ms Casey said.
The closing date for submissions on the proposed zone is July 23.