Bali Haque, chair of the Tomorrow's Schools Review Taskforce, which reviewed the entire school system for the Government two years ago, said the problem was the inevitable result of a failing system.
Haque was backed by other experts who said teachers could not reverse declining achievement without big changes to the way schools are run.
Their comments followed the Principals' Federation's call earlier this week for the Education Ministry to show more leadership in tackling declining student performance in a range of international and national tests.
Haque said the principals' criticism of the ministry was not surprising.
"This is a systemic problem and it's been cooking for a while," Haque said.
"If you set up a system where you're not providing national curriculum leadership, you're not providing national leadership training for principals, you outsource professional development, you invite schools to compete with each other, and then you provide minimal support from the centre and in so doing strip the ministry of expertise, which is what happened, it's hardly surprising that despite the amazing work that our teachers and principals are doing that we're getting this problem."
Haque said schools had been "left out to dry" and needed more support.
He said it was hard to believe that New Zealand had created a system where the ministry paid little attention to curriculum development and good teaching practice.
His review panel had recommended major changes including the creation of a new Crown organisation that would operate regional hubs to support schools and become responsible for hiring principals.
In response, the Government pledged in November 2019 to make changes including creating a new division of the Education Ministry that would give schools more support.
Haque said the Government's decision to set up a unit within the ministry was half the answer, but it would need to "have clout" and be staffed by people with a lot of experience in education.
He said he was not comforted by the ministry's announcement this week that it had commissioned an expert panel to review the maths curriculum, where achievement had been particularly poor.
"My worry is the ministry is going ad hoc again. It's picking up the maths curriculum, it's picking up bits of the problem and that's in my view really dangerous. What we need is curriculum leadership in the centre, in Wellington, which looks systemically at our curriculum, which reviews the curriculum, which looks at how it's put together, provides information and support for teachers across the board," he said.
"The problem is across the board we have a system that does not adequately support curriculum development, and does not provide good professional development and does not provide good leadership support for principals. That's where the problems are and we're not going to solve them by picking one at a time, we've got to solve them together."
However, the ministry's deputy secretary early learning and student achievement, Ellen MacGregor-Reid, said the process for changing the system, and reviewing the entire curriculum, was already under way.
"The commitment to change made in 2019 saw the Government broadly accept all the recommendations made by the Tomorrow's Schools Taskforce, including establishing a national Curriculum Centre. We have already recruited 40 health and wellbeing curriculum leads for this programme, she said.
'Disconnect' between national agencies and schools - Cathy Wylie
A member of the Tomorrow's School review team, a chief researcher at the Council for Educational Research, Cathy Wylie, said she backed principals' call for more support from the Education Ministry.
She said the debate over falling student achievement and the need for more central support for schools highlighted the urgency of acting on the review panel's recommendations.
Wylie said giving schools resources and leaving them to it was not working and the schools that were doing a great job needed help to share their work further.
"We have a disconnect between our, for want of a better word, our national agencies and the schools on the ground," she said.
"Just simply saying to schools 'here's money, go and find some support' doesn't necessarily mean they get the right support at the right time or find the right issues."
Wylie said schools needed to be able to work closely with an organisation that would monitor their progress and help them improve, and which also had "some clout" to make things happen.
She said the pandemic had delayed the Government's response to the review, which included the creation of a unit within the Education Ministry to work more closely with schools.
Wylie said international tests showed some decline in student achievement and also that some gaps in achievement between different groups of students were not improving.
"There are signs that the system isn't doing as well as we expect it to do. That's certainly been an issue for some time."
"It's good that the Principals' Federation is showing some concern about this and saying that we actually more support and guidance around this. That we need to work with the ministry and the ministry needs to work with us on it and it's not just a matter of having resources online, we actually need more on-the-ground advice and support if we're really going to change teaching."
Wylie said it would several years before changes to the school system resulted in measurable improvements in children's achievement nationally.
NZ may need 'to consider some alternatives' - Professor Brown
A professor of education and expert on educational assessment at the University of Auckland, Gavin Brown, said New Zealand might need to look overseas to find ways of changing its school system.
"More of what we already have probably won't make a difference. It seems to me we have to consider some alternatives," Brown said.
He said one option was Finland, which ensured its education policy worked in conjunction with other policies such as social welfare and also invested in high-quality teachers.
"Sure, they're a slightly richer society than us in terms of many other things but they have made a strong commitment that the poorest neighbourhood will have just as good a schooling experience as the richest neighbourhood and they've done that through exercising equity for all," he said.
Brown said he did not recommend copying high-achieving Asian jurisdictions such as Singapore, Korea and Hong Kong, which used frequent, high-stakes testing to raise average achievement.
He said those approaches created high levels of stress and left most students feeling like failures.
"You can get high average attainment by basically testing every kid every week in every subject and make those tests matter. The downside of this is children get shamed by not being number one, two or three, everybody else is a loser and I think that is hugely disheartening and discouraging," he said.
Brown said New Zealand's slide down various international testing schemes since the 1990s had been embarrassing, but this country still did reasonably well and he cautioned against putting too much stock in test results and ranking.
However, he said there was a big gap between what the New Zealand curriculum expected of children and what children were able to do.
Brown also warned against expecting too much of schools.
He said research showed they could affect about 25-30 per cent of a child's achievement, and the remainder was influenced by a child's home environment.
He warned that the Government should not reform the education system without also considering other parts of society.
"You can't separate educational practice and policy from social welfare policy, from health policy, you can't even separate it from employment policy so you can't solve educational achievement problems by just looking at schools and teachers and saying all we need is better teachers working in a better way," he said.
Education Minister Chris Hipkins said the Government's response to the review of the school system would be introduced over the next few years.
He said the changes to the history curriculum announced yesterday were the first of a series that would cover other curriculum areas.
"The New Zealand Histories is the first of what will be a significant change to the way our curriculum is constructed and that will touch all areas of the curriculum and we will be moving from one which is very loose, very broad, to something's that a little bit more prescriptive. We won't be going the whole hog of having a very prescribed syllabus, but we will be saying actually there are some things that shouldn't really be left to chance, that every school should be doing," he said.