Education Ministry figures show the communities around low-decile schools are poorer than ever but better educated.
Numbers calculated at Radio New Zealand's request show children at decile one schools come from neighbourhoods where half the homes are overcrowded and nearly half are in the lowest income group.
School principals say the figures show there is a growing gap between rich schools and poor schools.
School deciles are based on five indicators - parents with no qualifications, crowded households, household income, parents receiving income support, and parents with low-skilled occupations - in the neighbourhoods that each school's children come from.
Decile one schools are the 10 percent of schools with the most students from disadvantaged neighbourhoods as measured by those indicators. Decile 10 schools are the 10 percent of schools with the fewest.
The figures provided to Radio New Zealand show the median value for each of the indicators in each of the 10 decile groups.
At decile one schools, for example, the children come from neighbourhoods where the earnings in 41.7 percent of the households is in the lowest 20 percent once adjusted for the number of people; where 52.4 percent of the households are crowded; where 35.4 percent of parents have no qualifications, 33.3 percent receive income support; and 59.9 percent are in low-skilled jobs.
At decile 10 schools, in contrast, the students come from areas where the earnings in 9.9 percent of the households is in the lowest 20 percent; where 9.4 percent of households are crowded; where 5.7 percent of parents have no qualifications, 4.5 percent receive income support, and 22.3 percent are in low-skilled jobs.
Lower decile, lower income
The Ministry of Education said the figures were estimates and not all the indicators could be compared to previous years. However, the percentage of low-income households has risen for decile 1-4 schools since 2008, but fallen in deciles 5-10.
In decile one schools the figure has risen from 36.5 percent in 2003 to 38 percent in 2008 and 41.7 percent in 2015.
The principal of decile one Corinna School in Porirua, Michele Whiting, said she had seen that change happening in her school's neighbourhood.
"I have an impression that the area looks and feels poorer than it was even when I started here in 2006. There are a number of people that are leaving, either leaving the country or leaving the area to go north to find work. There's a sense then that there are fewer people and they're the ones who have least opportunities."
The chairperson of the PPTA's Principals Council, Allan Vester, said the increase in low-income households in the communities of decile one schools was worrying.
"That's of huge concern, I think that's the statistic that really is the concerning one ... the ability of those schools now to make a real difference is significantly harmed."
Mr Vester, who is principal of decile two Edgewater College in Auckland, said children from the poorest families often needed a lot of extra support.
He said there was a widening gap between the lowest and highest deciles.
"The availability of transport, the wealth of families, the ability to move students from school to school, has meant it's possible to get an ever increasing social division really. I think that must be of concern, I'm sure it's a concern to the Government."
Crowding linked to house prices
The figures show children at decile one schools are from neighbourhoods where 52 percent of households are crowded. That compares to 35 percent at decile two schools and just nine percent at decile 10 schools.
Principals Federation spokesman Phil Palfrey said that made sense given house prices in his part of Auckland.
"Around here the houses that used to be 10 years ago worth about $150,000 are now being sold for 450 upward, and so the peple who live in this decile one area would have to probably move in with each other to be able to afford the rent.
"I suspect it's happening on a larger scale than it was before," he said.
The figures show all deciles have fewer parents without qualifications, and fewer in the lowest skilled occupations than previously, and almost all have fewer parents on benefits. The exception is decile one, where 33.3 percent of parents receive income support compared to 33.1 percent in 2008.
The Education Ministry's head of evidence, data and knowledge, Lisa Rodgers, said operational funding was much higher for low decile schools because of the disadvantage faced by their students.
"For example, a decile one school gets approximately $900 a student or more in extra payment, and a decile two school gets approximately $600 per head in extra payments. For a decile one school, this top up funding averages almost one-third of the school's operational funding," she said.
"We also recognise the decile funding system isn't perfect, which is why there is a review of how schools are funded. That review is in its very early stages."