One in five schools needs intensive help and only 15 percent have effective teaching firmly established, the Education Review Office says.
It also warned nearly half the early childhood services it visited in the past financial year breached regulatory or licensing criteria.
The Education Review Office's (ERO) annual report for 2021-22 said 30 percent of schools it reviewed were in the "foundation" stage of establishing effective teaching, meaning they had a low level of maturity in that area.
About half of the country's schools had been reviewed using a new system of more frequent visits and only one-in-four had the conditions for sustaining high performance, it said.
In addition, one-in-five needed a lot of help to improve.
"Approximately 20 percent of schools in this group have been judged as requiring intensive effort across multiple domains to bring about improved learner outcomes," the report said.
The figure was slightly higher than the 18 percent of schools the 2018-19 annual report said needed intensive help.
ERO deputy chief executive for review and improvement Jane Lee said schools were generally doing well and the figures were comparable to previous years.
"It's not too dissimilar to what we have experienced over the past years," she said.
Lee said the responsibility for improving schools was shared across multiple agencies including ERO and was not a problem for teachers and principals to deal with on their own.
The pandemic had affected teaching and learning but schools had been very innovative in finding ways of keeping children engaged in learning, she said.
"Effective teaching from our point of view is where teachers know their learners well, they are using what they know about their learners to develop high quality learning programmes, they are using assessment and achievement data to plan forward in relation to students' needs abilities and interest."
Effective school leadership and governance created the conditions for sustained high performance including good use of data about student achievement, shared understanding of good teaching and learning, and ensuring equity for all learners and a safe environment, Lee said.
ERO was putting more emphasis on what mattered most for learning and it worked intensively with schools that needed help, she said.
Secondary Principals Association president Vaughan Couillault said he was not surprised the number of schools in need of extra help had not improved because the pandemic had made it harder for schools to get support.
"The ability for intervention to take place has been particularly stymied over the last couple of years."
The numbers needed to improve, Couillault said.
Principals Federation president Cherie Taylor-Patel said a factor contributing to the figures was that most principals were relatively new to the job.
"Sixty percent of school leaders have been principals for five years or less and if you think about that, for three of those years they've been coping with a pandemic where there was no guidebook to help them through," she said.
There had always been a group of schools needing extra help, Taylor-Patel said.
"It is concerning that it's now one-in-five schools needing intensive support. Is there capacity to deliver that? I'm not sure. Our system is really struggling to do all sorts of things just right now."
High non-compliance in ECE services
ERO manager of methodology Sandra Collins said the office was concerned about the level and nature of non-compliance in early childhood services.
The annual report said analysis of 541 reports found reviewers spotted problems with one or more licensing criteria at 41 percent of the services they visited.
The numbers were new because ERO reports had not previously noted regulatory breaches if they were rectified before the report was completed, Collins said.
"That is a shift for us which gives us a picture of what we found on-site and not just the non-compliances that are outstanding."
There were four regulatory standards and 97 licensing criteria which included things like displaying particular information or managing hazards and providing medicines, she said.
Most services were good at rectifying any problems when ERO pointed them out and only 14 percent of reports noted areas of non-compliance that still needed to be addressed, she said.
They included five percent of services where ERO staf found unacceptable risk to children.
"Most services are responding and often while we're there, working with them.
"Overall it's about five percent of the services that we reported on where we found unacceptable risk to children."
In those cases ERO informed the Ministry of Education and asked it to reassess each service's licence, Collins said.
The report said the most common areas of non-compliance included safety and hazard checking, emergency drills, excursions, and securing heavy furniture.