High schools in rich areas are so full they’re funding their own classrooms to take extra kids, while those in the poorest neighbourhoods are struggling for students.

A Herald analysis of classroom capacity at state schools across the isthmus has found a remarkably uneven spread of pupils, as parent choice and housing affordability continue to cause a headache for principals.

Numbers comparing teaching space to actual 2014 roll numbers at both primary and secondary level showed some schools were overflowing while others sat half-empty. Neighbouring schools differed widely in popularity and size, and each suburb had its own complex issues.

Among secondary schools in particular, there was a clear trend by decile. Schools in affluent areas were likely to be full-to-bursting, while many in poor suburbs had just half their classroom space in use. In total, there were 3146 spaces at deciles 1 and 2, while at deciles 9 and 10 the secondary schools were over the ministry-funded capacity by 1000 pupils.

Those figures did not include the three new high schools, which were not yet full.

Often, the most and least populated schools were right next door - for example on the North Shore high schools on one side of the motorway were all over-full, while on the other none had met capacity.

“What’s happening is that schools at the top of the food chain are attracting students and can maintain their rolls, but their lower decile neighbours are falling,” said Secondary Principals’ Council Chair Allan Vester, a principal at Edgewater College.

“If you’re slightly over or under that’s not a problem, but when the roll is trending down, you lose staff and that creates uncertainty, and you start to get an exodus. It can create a downward spiral.”

An example of that trend was Papakura, which was struggling to attract not just teachers but a principal, and to rebuild after a disastrous Education Review Office report earlier this year.

In contrast, popular schools like Mt Albert Grammar were so full they had to turn away kids, and were using locally-raised funds to add extra space on top of what the government provided.

“We are pretty popular,” said principal Dale Burden.

“There are a lot of families that are moving in to the area but lots that moved in when kids were younger. Families are thinking ahead to get in.”

At primary level, many schools were chock-a-block, with the government adding hundreds of classrooms to cope with the extra kids. In some areas, however, the Ministry of Education had declined school expansion plans and instead asked sought-after schools to think about zoning, to ensure more even growth as demographics continued to change.

Auckland Primary Principals' Association head Frances Nelson said form primaries, overcrowding was usually more of a worry than empty chairs.

“Primary numbers tend to be more cyclical - it waxes and wanes depending on who’s in the area, or where local early childhood centres recommend.”

One school, Rowandale Primary in Manurewa, had been over-subscribed by more than 100 kids this year, principal Karl Vasau said. Without a zone, it couldn’t turn anyone away and instead had classrooms crammed with kids. The ministry had provided some relocatable rooms, but they were yet to be completed.

“There are lots of families moving to Manurewa as it’s one of the last bastions of affordable housing,” Mr Vasau said. “But we can’t take everyone.”

The ministry of education’s Katrina Casey said schools did vary greatly in how full they were, and said that was driven by a range of factors including parental preference, the size of the local school-aged population, how conveniently schools are located to transport links, the teaching and leadership at a school, and what other schooling choices are available.

She said while there was a tendency for higher decile schools to be operating at high capacity, on average Decile 1 primary and secondary schools were 81 percent full, which was still “very high”.

“The size of a school doesn’t determine its educational performance – both large and small schools can be excellent,” she said.