Wales' performance in international tests for 15-year-olds has fallen further behind other UK nations.
The biggest drop was in maths scores with reading results also lower, while average science scores in the three-yearly Pisa (Programme for International Student Assessment) study were slightly up.
The tests were taken by a sample of teenagers in 91 countries and economies in 2025, and are seen as an important yardstick of how education systems are performing.
When results were last published in 2023, Wales' recorded its lowest ever scores in all three subjects.
The minister for education and Welsh language, Anna Brychan, said plans were in place to support schools to raise standards.
The Organisation for Economic Co-operation and Development (OECD) said the results showed Wales' "overall downward trend still continuing".
In Wales, 113 schools took part in Pisa with 3,406 pupils sitting the tests.
Welsh pupils' reading standards have been under scrutiny since the last set of Pisa results and scores fell again in the latest assessments, down from 466 to 459.
In the 2022 tests - the first after the pandemic - performance slumped in many nations but Welsh scores fell more steeply than the other UK nations.
It followed an uptick in the 2018 results.
Pupils at Ysgol Gyfun Gymraeg Glantaf in Cardiff took part in Pisa in 2025.
Caron, 16, said the test was different to usual assessments because they didn't revise for it and it was online rather than on paper "so that felt a bit weird".
"Depending on how you answered it it got easier or harder so it varied depending on how well you did."
Elin, 16, said: "Some of the questions were quite similar to what you might do in a science test, but some of the questions were quite random."
Unlike GCSEs, individual students don't get grades so Owain sad it "felt different".
"I don't think it was as serious," he said.
"When the questions got harder I backed out a bit, maybe gave a random answer."
Classmate Tiago said he enjoyed the experience of taking part in Pisa and knew that Wales had performed poorly in the past.
"Going in, I was excited because I really wanted to give it my all to boost the ranking," he said.
Headteacher Dyfrig Rees said it was important for schools to contribute to Pisa in order to give information about "how our teaching and learning compares to other countries".
He said it was one of a number of assessments for pupils doing their GCSEs.
"We do try and emphasise they should try their best, take their time and be focused but its secondary to other assessments in school life," he said.
He said he hoped Wales' new curriculum would ultimately lead to better results in Pisa.
"People are proud of the Welsh education sector, and they want it to be successful and so whenever there is a league table where we are not where we want to be -that's disappointing," he said.
More than 90 countries and economies took part in Pisa in 2025 with Asian countries and regions once again ranking highest including areas of China, Singapore and Japan.
But the UK featured in the top 10 for all three subjects and were described as "bucking the trend" of declining performance by the OECD.
However, Wales' performance was worse than England, Scotland and Northern Ireland and broadly in line with countries such as Spain and Croatia for both maths and science where it scored significantly below the average for OECD member countries.
For reading, it was on a par with Denmark and France and close to the OECD average.
In an extra test in this round of Pisa, Welsh teens also scored lower than their peers in other UK nations in computational problem solving.
Andreas Schleicher from the OECD said England had pursued "coherent and consistent policies in education" which were "conducive to producing good learning outcomes".
"That's not what we've seen in countries like Scotland or Wales to that extent," he added.
Though some of the decline in Welsh scores was not "statistically very robust" and science results had "stabilised", he said "unfortunately for Wales, we see that overall downward trend still continuing".
More than 760,000 students took the assessment in 91 countries and economies in 2025.
A sample of schools in each country are chosen to take part from which a representative sample of pupils are chosen.
Pupils are aged between 15 years, three months, and 16 years, two months - so usually in Year 11.
It's a two-hour online test and each student is tested in two subjects, getting different questions with variations in the combination and order of subjects.
There's also a background questionnaire which asks for information about the students, their homes and their school and learning experiences. School leaders also complete a questionnaire.
The OECD says Pisa "measures 15-year-olds' ability to use their reading, mathematics and science knowledge and skills to meet real-life challenges" and assesses the extent to which they have the tools "essential for full participation in social and economic life".
It claims results provide insight for governments on their competitiveness relative to other economies.
But some experts have questioned Pisa's value and the influence it has had in changing education policy.
After a big drop in the 2022 results the OECD said that "outcomes have largely stagnated or continued to decline in many countries".
Overall, the steepest decline was in reading displaying a long-term "weakening of performance" which predated the pandemic, the OECD said.
Schleicher said while "limited or moderate use" of digital devices for learning in school is often linked to better results, there were substantially worse outcomes when they were used for leisure in schools.
The OECD said key ways to improve education systems included having high and consistent expectations for pupils and to ensure teachers had strong teaching skills, not just subject knowledge, as well as using AI in a targeted way which did not replace "effortful learning".
Brychan reassured teachers and leaders that there would be no knee-jerk response to the results and plans were in place to support schools to raise standards.
"Let me be clear, these results are not where we want them to be. But in many ways, they reinforce what we knew already and highlight our need to improve standards of reading and maths, as a priority," she said.
Brychan said the Pisa results were not the only measure of performance and standards in schools, but that did not mean they should be "ignored", as "we take our performance in international studies incredibly seriously".
She added: "What matters now is what happens next and delivering on our promise to better support the education system to raise standards."
She said the Welsh government would be launching its Foundational Literacy and Numeracy Plan which represented an "important first step in the development of an equitable education system that works for all".
