The UK is still trailing behind leading countries at education and has made little progress since the last PISA rankings were published three years ago, the BBC reports.
The Programme for International Student Assessment (Pisa) provides education rankings based on international tests taken by 15-year-olds in maths, reading and science.
The Pisa rankings, run by the OECD, are based on tests taken by 15-year-olds in over 70 countries, and are an influential insight into a country’s educational performance.
The UK is behind top performers such as Singapore and Finland, but also trails Vietnam, Poland and Estonia.
The OECD’s education director, Andreas Schleicher, describes the UK’s results as “flat in a changing world”.
In maths, the UK is ranked 27th, slipping down one place from three years ago, the lowest since it began participating in the Pisa tests in 2000.
In reading, the UK is ranked 22nd, up from 23rd, having fallen out of the top 20 in 2006.
The UK’s most successful subject is science, up from 21st to 15th place – the highest placing since 2006, although science test scores have declined.
After the last round of rankings in 2013, there were warnings from ministers in England that results were “stagnating” – and reforms were promised to match international rivals.
But Russell Hobby, leader of the National Association of Head Teachers, warned that the results showed “a lost decade” in which the government had pursued an “obsession” with structural change which had “little impact on either standards or equity”.
Nick Gibb, England’s School Standards Minister, described the results as a “useful insight” and used the results to support the government’s expansion of grammar schools. He said the rankings showed the need to “make more good school places available” in grammar schools.
He also announced £12m to support professional training for science teaching.
The UK has remained among the mid-table performers, with Singapore rated at the top and most of the highest places taken by Asian education systems.
Within the devolved UK education systems, Wales had the lowest results in every subject.
Mr Schleicher said reforms in Wales had yet to make an impact and it was too early see if they would be successful.
At present Wales’ performance in reading puts it only a few places above parts of the UAE, Argentina and Colombia.
Education Secretary Kirsty Williams said: “We can all agree we are not yet where we want to be.”
But she said that “hard work is underway” to make improvements in Wales – and that it was important to “stay the course”.
Dylan William, of the UCL Institute of Education, urged caution on the Welsh rankings- saying changes took a long time to take effect and it could be another ten years before rankings would reflect what was happening at present.
England had the strongest results in the UK, but compared with previous years, Mr Schleicher said “performance hasn’t moved at all”.