More than 400 Victorian primary schools are rolling out a new year 1 numeracy check next term — a 15-minute one-on-one test designed to catch kids falling behind in maths before the gap gets too wide.

The check, which becomes mandatory in all public primary schools from next year, tests what experts call "number sense" — things like ordering numbers, comparing amounts, and recognising groups. It's not just about counting or basic sums.

It comes alongside the year 2 reassessment for students who didn't meet the benchmark in last year's phonics check. So schools will get fresh data on both literacy and numeracy at the same time.

Kelly Norris, manager of early numeracy research at the Centre for Independent Studies, called the checks a "strong first step".

"However, identifying children at risk isn't enough on its own. It's what we do next that really makes the difference – whether that identification leads to timely and effective support for those children," she said.

Norris pointed out that while Victoria does relatively well compared to other states, Australia's overall performance in international maths assessments has been sliding for years. A Grattan Institute analysis last year found one in three school students fail to reach proficiency in maths. In Victoria and the ACT, nearly 30 per cent of students weren't proficient in NAPLAN numeracy.

"The goal isn't just to find students who are struggling, but to provide support early enough to prevent small gaps in number sense from becoming entrenched achievement gaps later on," Norris said.

Maramba Primary School was among the first to trial the check last month. Principal Moniba Ehsan said the test, along with the phonics check, has already helped identify about 10 students per cohort of 30 who could benefit from extra support — and a handful of high achievers too.

"The teachers noticed some of the questions the kids were having difficulty with, so they've incorporated that in their daily [revision exercises]," Ehsan said. "We noticed there were some things that the teachers assumed that the kids knew and understood, but when it was phrased in a particular way, the kids were baffled."

Maramba's NAPLAN results are tracking close to average compared to similar schools. Ehsan expects that to improve as the checks catch gaps earlier.

But not every school is jumping in. Some principals are waiting until the check is mandated, saying it's a strain on already stretched resources.

Kate Buck, principal of Brandon Park Primary School, said the one-on-one format means her school would need to hire casual relief teachers for six days just to test year 1 students. That costs money — even if the department covers it.

"When you look at it business-wise, you're talking about money as well ... I'm sure that the department will say they'll cover CRT costs, but is that a valuable way to spend money with those kinds of other assessments that you could use to get the same data?" she said.

Buck's school already uses PAT maths testing. She acknowledged the numeracy check would give a consistent comparison across Victorian schools, but questioned whether it's worth the extra cost and time.

The Victorian government says the check is evidence-based and aligned with the state's revised curriculum. It's designed to be quick — about 15 minutes per child — and to give teachers useful information without taking up a whole morning.

Norris said numeracy checks have the potential to be less time-intensive than older assessments, but individual administration is still a costly choice.

"The goal with a numeracy check, ideally, is to get the most useful information in the least practical time," she said. "It will be interesting to see how well the Victorian year 1 numeracy check achieves that goal."

For now, more than 400 schools will give it a go next term. The rest will have to wait until next year — when it becomes compulsory.