Every three years, the OECD tests around 750,000 fifteen-year-olds across dozens of countries on the same scale. This year's results, released this month, are the most worrying it has ever recorded, and, for many teachers, a real wake-up call.

The headline is bleak. Across the wealthy world, reading and maths have both fallen to their lowest averages ever recorded (maths 463, reading 461). Reading alone is down about 28 points since 2015, which the OECD calls roughly a year and a half of lost learning.

It is not simply the pandemic. Reading and science had been sliding for a decade before COVID. Today one in five teenagers is a low performer in all three subjects at once, up from one in six in 2022. Too many quietly slip through the cracks before anyone notices.

Screens are part of the story. About a third of students say they are distracted by devices in class, and those glued to screens for five to seven hours a day score around 49 points lower in maths than those who keep it under an hour. And where you live still matters far too much: a child's results are strongly tied to family wealth and postcode, so genuinely fair systems, offering anything like a level playing field, remain the exception.

But it is not all doom. Singapore and the Chinese provinces are still top of the class, Estonia leads Europe by pairing strong results with real fairness, and England's science climbed to its highest since 2012. What the leaders share is unglamorous: they protect their teachers, sort children into tracks late, and keep a reading culture alive.