The most recent PISA results - which compare achievement in maths, science and reading among 15-year-olds across the world - were released last week, painting a grim picture of Wales' education system.

But how useful is the system for determining how well youngsters are being taught?

IAN CRAIG looks into the issue.

ONCE again Wales has ranked behind the other three nations of the UK in a global programme testing the achievement of 15-year-olds.

The latest Programme for International Student Assessment figures were released last week, showing, while Wales has improved slightly compared to previous results in 2012, it still lagged behind England, Scotland and Northern Ireland in all three subjects assessed - science, maths and reading.

But the test, which was introduced in 2000 and is held every three years, with around 540,000 youngsters taking part each time, has proven controversial, with some claiming

Newport City Council member Sally Melwa, who has worked in education for more than 30 years in a number of roles, said she believed the results needed to be “taken with a pinch of salt”.

“It is useful for a comparison, but it is not the most useful comparison,” said the councillor..

She added she believed its usefulness was limited by the way it compares differing education systems as if they are identical.

“For example Singapore is the top country, but it also has one of the highest suicide rates among young children,” she said.

“Two a week kill themselves because of the pressure they are under.

“If that is what it means to be number one do we want to be number one?”

Cllr Mlewa said she was also concerned the test places an undue weight on English, maths and science while marginalising the more creative subjects.

“You can teach the context and you can teach someone to pass an exam,” she added.

“But understanding is different thing.

“People who are academic are good at that. Children who are not as academic may understand what they are doing but may not be able to express it right.”

She added: “We’ve got to measure more than just passing exams. "Passing exams is not education.

“If I have a leaky pipe what I need is a good plumber, not someone can write me an essay.”

Headteacher at Newport's John Frost School, formerly known as Duffryn High, Jon Wilson said he remained yet to be convinced of the usefulness of the test.

"It is useful, but it's only one tool," he said.

"Only a fool pays attention to just one test."

But he said he was in favour of the approach of testing the ability of young people to apply practical skills in a number of areas.

"In a skills-based curriculum it is useful to have a way of testing these skills," he added.

"But in terms of how helpful it is to youngsters themselves, I am not sure.

"And there are question marks over just how coached children in some are to pass the test."

He added he was concerned undue weight was placed on the results of the test, saying: "It seems to me we put all our eggs in the PISA basket and there is a whole range of issues facing education in Wales."

Of the 72 countries taking part in the study, Wales fell roughly in the middle, ranking 35th for science, 39th for maths and 40th for reading.

Although this represents an improvement of four places for maths and one each for the other two subjects, the country is still far behind Welsh Government targets.

In 2012, then-education minister Leighton Andrews set a target of Wales being in the top 20 countries in the world by 2015. But just two years later his successor Huw Lewis dropped the pledge.

With both men leaving the Senedd following May's Assembly election - Mr Lewis stood down with Mr Andrews having the dubious distinction of being the only Labour AM to lose their seat - the education portfolio was handed to sole remaining Liberal Democrat AM Kirsty Williams.

Speaking in the Senedd last week Ms Williams said she recognised the system was contentious, but remained convinced it was a valuable tool.

"It remains the recognised international benchmark for skills," she said.

"Countries around the world use it as a signal to entrepreneurs, employers and investors."

She added: "We do need to see it as an important test, not of individual schools and not of individual pupils, which is what GCSEs are about, but it is a reflection on the health of our system as a whole."

Welsh Conservative education spokesman and Clwyd West AM Darren Millar said he believed the ranking were an important tool.

“They provide an international benchmark for the performance of our education system which can impact on investment and employment in future generations,” he said.

But his Plaid Cymru counterpart Llyr Gruffydd said he “(does not) feel that the (education) sector in its entirety is buying into PISA”.

And Labour AM for the Cynon Valley Vikki Howells said she was not in favour of the system, calling it "a crude educational measure, bearing, in many respects, little relation to the skills required for GCSE."

"GCSEs are quite rightly the focus of teachers and students at the age of 15, and these are the measures that, in reality, lead to the qualifications that have a direct impact on our students’ futures," she said.

Asked if the Welsh Government was considering reforming the country's education system in light of the results first minister Carwyn Jones said he did not believe this was the way forward.

"We do know that, in other countries where improvements were effected, those improvements do take years," he said.

"Improvements cannot be turned round within three years.

"Of course we take responsibility.

"We were the government who actually went into PISA in the first place.

"We must accept that PISA is a way in which the education system of Wales will be measured."

But he conceded “there is more work to be done”.

“We are seeing improvements in some areas, but, no, things are not as they should be, and we’ll never be content,” he said.

“We’ll always want to see improvement in the Welsh education system, and that’s exactly what we wish to see and we will do.”

In line with previous trends, Singapore, Hong Kong and Japan topped the tables in the most recent results.

To view the full results visit gov.wales/statisticsand-research/achievement-15-year-olds.