Fewer pupils in a classroom means a better education: that for decades has been the thinking among parents and politicians.

But according to the OECD, it makes no difference at all whether there are 20 or 30 children in a class and in fact larger class sizes might even be better.

Just look at South Korea, it says, whose school leavers often learn in groups of 35 or more, and are increasingly finding their way into top universities both here and in America.

Seoul correspondent Lucy Williamson unpicks the paradox.

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