Research is pointing to a consistent achievement gap between children in lower and higher decile primary schools equivalent to an average two years of schooling.
The two-year gap has shown up in just-published assessment results in reading and social studies, and in earlier tests of maths, health and PE, science and writing.
The gap is between average scores for children in decile one, two and three schools, and those of children in deciles eight, nine and 10 as measured by the National Monitoring Study of Student Achievement.
The study found that in term three of the year they were tested, nearly 60 percent of Year 4 and Year 8 children were reading at the curriculum level expected by the end of that year.
But when looked at by decile, only 38 percent of Year 4s and 41 percent of Year 8s in low-decile schools were at or above the expected level compared to 72 percent of Year 4s and 70 percent of Year 8s in high-decile schools.
Similar results were evident in social studies for Year 4s. However, for Year 8s, just 17 percent of children in low-decile schools were at the expected curriculum level compared to 54 percent in the high-decile schools.
The monitoring study is run by the Educational Assessment Research Unit at the University of Otago and the Council for Educational Research (NZCER)
The co-director of Otago's research unit, Alison Gilmore, said assessments of four other curriculum areas - maths, health and PE, science, and writing - had found similar gaps in achievement between deciles.
It was likely a two-year achievement gap between children in low and high decile schools was persistent across all subjects.
"By next year we will have assessed across the whole curriculum and will be able to make comparisons and see what trends are across learning areas, but I expect it will be reasonably persistent."
Associate Professor Gilmore said the gap in achievement was significant and needed to be addressed.
"These differences have been long-standing. It's disappointing to see that they're still there. But I think it provides further evidence that there is something we need to do to address this disparity."
The impact of school decile was conflated with ethnicity, because Māori and Pasifika children had lower average scores than New Zealand Europeans and were over-represented in lower decile schools.
Associate Professor Gilmore said there were high-achieving children in low-decile schools and low-achievers in high decile schools.
The manager of assessment design and reporting at the Council for Educational Research, Charles Darr, said the achievement gap between the deciles was smaller in reading than it was for social studies.
That could be because schools were putting more emphasis on reading than social studies, he said.
Results don't surprise education leaders
Educational Institute president Louise Green said out-of-school factors played a huge part in children's achievement, but schools could do a lot to overcome the achievement gap.
"It can be overcome as long as there's good levels of resourcing to support it," she said.
Principals Federation president Iain Taylor said he was not surprised by the two-year achievement gap.
"Some students come to school not ready to learn, so before they even put their foot in that classroom they are behind the eight-ball to start with."
Mr Taylor said the gap could have been higher.
"I know in my own school we have students starting who can be three to four years behind...when they start at Year 7 level. So two years by the end of that time, I suppose it's pretty accurate."
The Education Ministry's acting deputy secretary for early learning and student achievement, Karl Le Quesne, said socio-economic disadvantage played a role in school achievement. The ministry was not aware of any evidence that low-decile schools provided a lower quality of education.
Mr Le Quesne told Morning Report some children start school behind their peers, but they can be caught up with good teaching and leadership, and by engaging them in their learning.
"We can't change how they arrive but we can have a really big impact on their learning once they are in the education system."
He said secondary schools are becoming increasingly sophisticated in using data to identify individual students at risk of not achieving, and providing them with the support they needed to reach their goals.
Programmes like Pasifika PowerUp have also supported these students in attaining NCEA.
"As a result we're seeing achievement rising for these students at a faster rate than other students, and a narrowing of the achievement gap with other students," he said.
Research had established that factors that collectively had a much greater impact on student achievement than socio-economic disadvantage included the quality of teaching, performance expectations, school leadership, and positive relationships between parents and teachers that focused on learning, Mr Le Quesne said.
- 58 percent of all Year 4 students reading at or above expected level
- 59 percent of all Year 8 students achieving at the level expected
- 63 percent of all Year 4 and 38 percent of Year 8 students performing at or above expected level for social studies
- Girls scored higher than boys in reading by a margin equivalent to roughly one-year of learning.
- Students who reported more absences and instances of being late for school scored lower on average in reading than students who reported fewer absences and instances of lateness
- Children from low-decile schools, and Māori and Pasifika students reported more frequent instances of whole-day absence and being late to school than other students.
- Students who 'always' spoke English at home scored higher on average than students who spoke English 'often' or 'hardly ever' at home.