In the mid 1990s a series of tests were administered to large samples of the adult population in many OECD countries. This was the International Adult Literacy Survey (IALS). Because the tests were identical across all countries, they are a valuable source of information. Surveys such as these are regularly given to schoolchildren, but the IALS has been the only such survey for British adults.

Several features of the IALS results are worth noting. First, the average scores of the top 20 per cent do not differ greatly across most countries. By contrast, the average scores of the bottom 20 per cent differ dramatically.

Second, there is a very high correlation between the dispersion of test scores and the dispersion of earnings in a country—well over 80 per cent. Putting this another way, countries which do a good job of educating individuals at the lower end of the ability range