Why does Estonia and Poland score so well in PISA?

From the Economist, the correlation between teacher salary and teaching hours, and learning outcomes (as measured by PISA score).

The variation is very interesting. The surprises are Estonia (526) and Poland (521), both of whom achieve close to the scores of PISA leaders (outside the Greater China), South Korea (542) and Japan (540). So the question should be, how do Estonian teachers achieve better PISA outcomes than their counterparts in Holland who are paid five times more, or in Canada, who also work a third more? Is there a cultural dimension to teaching and education in Estonia and Poland, like with Finland, that contributes to their disproportionately superior performance? Or, is it more institutional design and governance improvements that are behind this success?

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