Compulsory tests will ensure fewer children fall through the cracks at school, says Education Review Office head Nicholas Pole.

Earlier this month, the government announced mandatory reading, writing and maths tests for primary schools.

From next year, schools will be required to test the ability of five year olds to link sounds and letters at 20 and 40 weeks of schooling, while schools will also have to test reading, writing and maths twice a year for children in years 3-8.

Nicholas tells RNZ the schools' watchdog has been telling teachers for decades to improve their use of tests.

He says despite these warnings, too many schools still don't use assessment effectively to check children's progress, inform the next steps in their learning, and inform parents.

Nicholas says the government's decision to mandate twice-yearly tests for children in Years 3-8 will help primary schools lift children's achievement if it's done well.

"The evidence is pretty clear that when you're doing this coherently, consistently and systematically, it does help you as a system identify those learners who are most at risk of failing.

"It has again some lift in overall system-wide performance, but that's got to be matched with shifts in teaching practice and in shifts in the deliberateness of what's going on in schools. So here we're talking about building teacher capability and confidence, ensuring high expectations for every learner, having great resources to support teachers and having the strategies that support those kids who will be struggling."

Nicholas says there has been some improvement in schools' use of assessment, but there's still a system-wide lack of clarity about which tests to use and how to use them well.

He says the problem is contributing to long-standing underperformance by some children.

"One of the worrying features in our system is that we have one of the highest rates of within-school variation in student achievement among OECD countries. This suggests to us that we are failing to identify adequately or support those who are falling behind in our schools and assessment is clearly one of the elements of defence in this."

Nicholas says ERO will expect to see teachers using the twice-yearly tests to check students' progress, inform what they teach next, and identify those who are struggling.

"From ERO's perspective assessment is so integral to the teaching and learning process. It helps teachers understand what students are learning. It measures teachers' impacts on student learning, and it helps teachers in giving critical feedback to students in the learning process."

He says ERO will use schools' test results to check their performance.

"The data allows us to pinpoint how well the school's doing and sit down with the school and discuss how they understand their data, how they are responding to their particular learners' needs, whether there's any particular group of learners who are being disadvantaged and struggling to proceed and what might be some of the strategies that the school could think about or work on.

"That also helps identify whether or not there are particular gaps in teacher competencies that the school can look to doing further professional learning and development, or having greater support with teaching practice."

Some teachers are warning that the move to regular tests could demotivate children who are repeatedly told they are performing below the expected level for their age.

But Nicholas says teachers should be able to tell their pupils how they are performing without causing disappointment.

"Good teachers do it every day and you know I I just love going into schools where kids can sit down with me and tell me about 'this is where I'm at in my reading or where I'm at in my maths and this is what I've got to do next, and I will know that I've achieved this when I can do the following'. Great schools and great teachers do this as a matter of course," he says.

-RNZ.