There's an assertion higher decile schools only appear to be doing better because they get more students from well-educated homes.
The New Zealand Initiative is disputing the Tomorrow's Schools' claim that the quality of our schools varies significantly.
It's analysed data for 400,000 students over the past 20 years. Executive director Dr Oliver Hartwich says the research shows that inequality in the education system isn't down to some schools doing a poorer job.
He says it's due to the different backgrounds of the students they get.
Hartwich says basically that means Decile 10 schools aren't actually performing better, they just have more students from well-educated homes to work with.
"When you have students coming from background where they've been read to, they have books in the house, they have extra curricular activities, of course they are performing better than other students where they were not being read to and there were no books in the house."
Secondary Principals Council chairman James Morris supports the research. He told Mike Hosking it's because lower decile
schools get extra resource.
"Students that go to those schools, a smaller proportion of them seem to be able to achieve well. So what can we do to make sure those lower socio-schools have what they need to do an even better job then they already do."
However, he doesn't think we should equalise school funding across the board.
Morris says it's important lower decile schools get more resources, as they have to work harder to achieve their results.
"There's only three per cent of school funding that actually is made up in funding difference. A lot of the overseas research shows that you need six per cent or more to make a significant difference."