A Herald investigation has found deep disparities hidden beneath rising high school pass-rates tied to students' socio-economic status and ethnicity.

Data shows that despite record numbers of students gaining the National Certificate of Educational Achievement (NCEA) last year, at every step Maori, Pasifika and low decile students are getting a different kind of NCEA to students from more affluent, Pakeha and Asian backgrounds.

Official statistics on all standards sat in every subject for 2015 show:

• Maori, Pasifika and low decile students were less likely to take academic subjects than Pakeha, Asian and high decile students.

• When they did take academic subjects they were less likely to pass

• They were less likely to sit exams, and when they did, their marks were less likely to include "Merit" or "Excellence" grades

• Maori, Pasifika and low-decile students were more likely to be enrolled in "vocational" subjects, which were not university-approved

For Maori students in particular, the proportion of academic standards entered dropped off steeply depending on decile. At decile 1, 44 per cent of Maori entries at Level 2 were in academic or "achievement" standards, the lowest participation rate of any group.

In some subject fields, the differences between decile and ethnic groups were particularly noticeable.

In science at Level 2, for example, entries for decile 10 Asian students were 30 per cent, while entry rates for Maori at decile 1 were just 8 per cent.

Conversely, at Level 2, decile 1 Maori students were four times as likely as decile 10 Pakeha to take subjects in the "services sector" field - an area including hospitality, tourism and retail. Popular standards in this field included cooking food by grilling, and preparing espresso-based drinks.

Maori and Pasifika students tend to dominate low-decile schools, while Pakeha and Asian students make up the bulk of high-decile students. Across all deciles, 14 per cent of Maori students studied Level 2 science, compared to 28 per cent of Asian students.

The data was detailed enough to show that even where students took the same subjects, their entries differed. For example, in English, more low-decile students took a test about a film; whereas more high-decile students were assessed on a written text, like Shakespeare.

Earlier this year, education minister Hekia Parata celebrated record growth against the government target of having 85 per cent of 18-year-olds with Level 2.

Pass rates grew by more than 10 per cent in just five years, to 83.5 per cent. Maori and Pasifika achievement increased most, while remaining below other ethnicities.

However, Labour education spokesman Chris Hipkins said the more detailed data showed the target was "meaningless".

"You can get to the target in many different ways that don't leave kids better off at the end of it," he said. "All it's doing is reinforcing a class division. But kids' abilities aren't determined by their socio-economic status."

Dr Earl Irving, from the Starpath project, said ideally, all students would be given the opportunity to stretch their minds.

"It's not that all youngsters from low-decile schools are going to go to university. It's making sure that those are capable of doing it do get the chance," he said.

"Otherwise you risk ending up with a low-wage economy. Yes, they can get a job, but what about their lifetime outcomes?"

Dr Aaron Wilson, the co-author of a University of Auckland paper about similar trends, said the fault was partially with the qualification design.

"NCEA's greatest strength and greatest weakness is it's flexibility," he said. "It can be used to recognise strengths and open doors, or pigeonhole kids and limit their pathways."

Education minister Hekia Parata said the data didn't show anything she didn't already know, which was why she had supported Maori and Pasifika with a raft of new programmes.

"We recognise that there is still more to be done and we are focussed on that. But that shouldn't mean that we don't celebrate the achievements already taking place."

Ministry of Education deputy secretary Lisa Rogers said it was working to address the inequities, with regional teams working directly with schools.

She said NCEA had helped Maori and Pasifika students stay in education longer, "a key first step in improving education outcomes".

"It has also enabled more students, including this cohort, to leave school with the skills, knowledge and disposition required to help them gain employment."

The ministry was monitoring the the trends in the data, Rogers said.

Subject-level NCEA trends used to be available online, but the data was removed by NZQA for privacy reasons in 2013. The Herald obtained the data through an Official Information Act request.​