The roll of Wanganui High School has grown by more than 350 students since 1999, despite an enrolment scheme implemented that year to prevent crowding.
And since 1999 the Education Ministry has spent more than $2.5 million to accommodate the extra students.
Those numbers were supplied by Marilyn Scott, Ministry of Education acting manager of education, curriculum and performance, after a request the Chronicle made under the Official Information Act.
The Wanganui High School (WHS) roll was at 1720 this year, after peaking at 1730 in 2009. This year Wanganui's other state secondary schools - Wanganui City College and Wanganui Girls' College - have rolls of 410 and 371 respectively.
But High School is widely considered as the superior school in Wanganui and its NCEA results almost match those of the prestigious Wanganui Collegiate School. WHS often has a student waiting list, and real estate agents advertise houses as being within its zone.
While it is bulging at the seams, Wanganui's other state schools both have spare capacity.
Ms Scott said it was Government policy not to invest in additional buildings at one school without taking into consideration the management of the wider network of neighbouring schools - but from her figures it appears the enrolment scheme has not had the desired effect.
The schemes were intended to prevent crowding, make sure students were chosen fairly and transparently and make the best use of the existing school network, she said.
The WHS enrolment zone was chosen in 1999, in consultation with other schools. It takes in St John's Hill, Springvale, College Estate and parts of Gonville, and excludes Aramoho, Castlecliff, central Wanganui and Wanganui East.
It has been reviewed every year since then. It could be changed, with another consultation process, but the school would still be able to enrol as many students as it now has capacity for.
Ms Scott said there were many imbalances of roll numbers and school capacity in New Zealand. She attributed that to schools not always being built in the places where population was growing. Reorganisation could sometimes remedy the imbalances, for example if one school decided not to take students from a particular year, leaving them for other schools.
That seems an unlikely prospect, at a time when state schools are competing with each other for student numbers and the resources they bring.
All of the city's secondary schools are feeling the pinch this year, because due to a fluctuation in population there are about 200 fewer secondary school students in Wanganui than there were in 2009. WHS has 50 fewer than 2009, Wanganui City College has 90 fewer and Wanganui Girls' College has 10 fewer.
However, the fall in roll numbers is not about to repeat itself in 2013.
Throughout the wider Wanganui roll area numbers were staying on an even keel at most schools with just two or three looking at more enrolments for next year.
Wanganui Collegiate School is expecting 30 more students next year. The roll was predicted to jump from 420 to 450.
Registrar Alan Richardson said they were already preparing the advertising for new staff positions.
Wanganui High School predict it will stay around the 1720 mark, City College said it is looking at around 430 again, Wanganui Girls' College said at this stage it could gain a few more but were looking at about the same again of around 380.
Cullinane College was hoping its roll would rise from 268 to 300 next year.
Outside Wanganui, Turakina Maori Girls' College in Marton was keen to raise its current roll from 96 to 100 in 2013, Nga Tawa Diocesan School for Girls is steady at 290 and Rangitikei College is looking at around 320.
Taihape Area School's roll is looking steady for 2013 at 320, and Patea Area School hopes to have 140 on its 2013 roll. This year the roll stood at 138.
Projected rolls for 2013