From their first day in the classroom, children from poorer backgrounds are more likely to fall behind in reading, writing and maths.
National standards from primary and intermediate schools from across the country shows pupils at lowest-decile schools are more likely to perform below national standards than those at the highest-decile schools.
The figures have prompted calls for real efforts to improve inequality.
The Dominion Post and other Fairfax Media outlets published results from more than 1000 schools nationwide at the weekend.
Principals Federation president Paul Drummond, who remains staunchly against the national standards in literacy and numeracy, said data obtained by Fairfax Media at least confirmed the "very strong correlation between student achievement and socio-economic status".
"This highlights the fact that if we want to improve and lift achievement and learning in our schools across all things, then we have to make a really genuine effort to improve equity," Mr Drummond said.
"Maybe this will be the catalyst for a stronger Government response around those equity issues. It has been worthwhile in confirming those correlations, but we knew that before national standards."
At the decile 1 Tairangi School in Porirua, it was against the odds that 76 per cent of pupils were at or above the standard in reading.
Principal Pip Newton said poverty was a problem among the school's pupils, but that did not mean they could not achieve in the same way as their peers at higher-decile schools. However, getting to the same level might take longer.
At the decile 10 Worser Bay School in Wellington, principal Jude Pentecost said good results were not simply due to pupils coming from wealthy backgrounds. The school's staff and structure also played an important role.
Andrew Wilson, board of trustees chairman with two children at the school and a third starting next year, said: "Parents tend to be well-engaged, and interested in their children's learning and wellbeing. We're not having to deal with issues like kids coming to school without breakfast.
"There's no question that there are benefits [of being in high-decile area]: there's a preparedness, and a willingness amongst the parental community to take an active interest. If you're holding down two or three jobs, that gets a whole lot tougher."
The 69 decile 1 schools that returned data to Fairfax had a much higher proportion of pupils not meeting the standards compared with pupils from decile 10 schools. Just over half (52.3 per cent) of pupils at decile 1 schools did not make the writing standard. Of the 135 decile 10 schools that sent data, the proportion not making the writing standard was only 20.3 percent.
In reading, the gap between decile one and 10 pupils not making the standard was 30.9 percentage points. And in maths the gap was 31 percentage points, with nearly half (47.6 per cent) of kids at decile one schools not meeting the standard compared with 16.3 per cent at decile 10 schools.
The national chairman of the Quality Public Education Coalition, John Minto, said the socio-economic divide in education achievement was the "elephant in the room" from the national standards results.
"The inconvenient truth for Education Minister Hekia Parata is that the strongest indicator of student achievement is the socio-economic background of their families," Mr Minto said.
"The Government now has no excuses for ignoring child poverty and allowing income inequality to increase."
Ms Parata said the Government wanted the results from the standards to drive "an outbreak of student achievement".
"Actually, student achievement is pretty good but for New Zealand, all learners achieving to their fullest potential is what our aspiration is," Ms Parata said.
- The Dominion Post
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