One ploy schools guard against is parents arranging to live temporarily within zone to enrol their child, either through a rental or swap agreement.
Auckland Grammar has had two cases where annulled enrolments were reviewed by the ministry this year, and had seven such cases last year. The school has a fulltime enrolment registrar and requires parents to hand over documentation that can include power bills to prove their residency.
However, with its zone adding hundreds of thousands of dollars to property prices, checks are also made throughout the year.
Ten out-of-zone students were picked from a ballot of around 200 this year, and headmaster Tim O'Connor said some families try to find another way in.
The law allows for enrolments to be annulled if it is discovered parents used a false or a temporary address to enrol a student.
Grammar has adopted a strict definition of "temporary" under which a student moving out of the zone during their schooling faces annulment.
Mr O'Connor said decisions were made on a case-by-case basis and there could be circumstances which meant a student could stay. Parents were also encouraged to make early contact about possible moves.
"The fact for us is the volume of demand, and people's desire to get into Grammar. And what some will do to achieve that aim.
"We need to be fair to all, so we do and will continue to be stringent in our application of the rules."
Mr O'Connor said the school looks at rental agreements closely to try to head off issues before students are enrolled. A one-year rental agreement would not be satisfactory.
Last year, a private investigator was used to door-knock a residence at a range of times and dates to check a student was living there.
Contentious enrolments are not limited to secondary schools. Gladstone School in Mt Albert had six cases reviewed last year and three this year.
Principal Dave Shadbolt said in all of the reviewed cases the board of trustees determined that students had only lived in zone for a short time prior to enrolment, and then moved out of zone.
All the annulments were upheld, Mr Shadbolt said, although one student this year had moved back within zone and rejoined the school.
Yesterday the ministry said just one of the 46 annulment reviews since 2011 was reversed.
The ministry figures are only cases that have been reviewed, although Auckland Grammar said the numbers reflected all of its annulment cases.
The true number of families attempting to beat the rules is higher, with other schools such as Ellerslie School and St Heliers reporting they fend off numerous bogus applications each year before students are actually enrolled.
The strength of feeling about zones was demonstrated last week when the Herald revealed that One Tree Hill College and Selwyn College had backed down from plans to have new proposed zones overlap with those of Grammar and Epsom Girls Grammar.
Residents in shared zone areas were assured they would be able to choose which school their children attend.
But some believed it might be a first step to their eventual exclusion from the "double grammar zone", and submissions were overwhelmingly hostile to the proposals.
