The Paris-based Organisation for Economic Cooperation and Development said it had seen some of the steepest drops in performance since 2000 when it began its usually triennial tests of 15-year-olds reading, maths and science skills.
On average across the OECD, one out of four 15-year-olds tested as a low performer in maths, reading and science, which means they could not use basic algorithms or interpret simple texts, the study found.
Poorer results tended to be associated with higher rates of mobile phone use for leisure and where schools reported teacher shortages.
The OECD said the decline was not inevitable, pointing to Singapore, where students scored the highest in maths, reading and science, with results that suggested they were on average three to five years ahead of their OECD peers.
After Singapore, Macau, Taiwan, Hong Kong, Japan and South Korea also outperformed in maths and science, where Estonia and Canada also scored well.
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