Auckland Grammar old boy John Chisholm wants his sons to go to a good single-sex school like he did - but they don't live in the right zone.

So the next best option for the St Mary's Bay family is to try their luck at Auckland Grammar, a school Mr Chisholm enjoyed attending in the 1970s.

"The only school we are zoned for is Western Springs [College], which I believe is quite a good school, but it's co-educational. I think it's important, particularly for boys, that they learn in a single-sex environment."

Choosing Grammar as his next option for 12-year-old Harry - and later for 9-year-old Angus - comes back to his own time at the school, which he says has a good all-round reputation.

"I got a lot out of the school, particularly from an academic and sporting perspective, and I think my son, and also my [youngest] son are that way inclined as well ... so really it's an opportunity that I'd like to present my boys with."

While out-of-zone positions at the highly sought-after decile 10 school are few, changes to enrolment rules mean Mr Chisholm's children have a slightly better chance of selection than in previous years.

While some say giving priority to children solely because of the school their parent attended is unfair, it's a position he is happy to be in for the sake of his sons' education.

"We are very much in favour of it, anything to give you an advantage over the next guy is probably worth taking isn't it?"

Last year Grammar received about 300 out-of-zone applications for just 12 Year 9 places - which are drawn from a ballot according to the list of priorities. The number varies from year to year and it is too early to know how many will be available for 2012.

Mr Chisholm is aware there are others ahead of his son but says at least the rule change puts Harry onto the priority list for next year.

If Harry gets in, it will be easier for Angus as siblings of current students are second on the priority list.

"We believe a public school education is very important," he said. "Unfortunately we can't achieve what we wanted in our local area."