Money alone can't buy a good education system. It's what you do with the cash that counts, according to the latest education report from the OECD's Programme for International Student Assessment (Pisa).
Investment in teachers and acting on a belief that all children can succeed in school are the strongest drivers in educational success, it concludes.
The report argues: "As many OECD governments are poised to trim public budgets and cut expenditures, parents, educators and policy-makers can take some comfort from Pisa findings that show the success of a country's education system depends more on how educational resources are invested than on the volume of investment. The countries that are the strongest performers in Pisa are not the wealthiest, nor do they allocate more money to education."
Beyond a threshold of US$35,000 (pound;22,000) spending per student, expenditure is unrelated to performance. For example, countries that spend more than $100,000 per student from the age of six to 15, such as Luxembourg, Norway, Switzerland and the US, show similar levels of performance as countries that spend less than half that amount, such as Estonia, Hungary and Poland. Meanwhile, New Zealand, a top performer in Pisa, spends a lower-than-average amount per student over the same period.
The strongest performers are those who invest more in teachers. For example, lower-secondary teachers in Korea and Hong Kong - two high performers in the Pisa reading tests - earn more than twice the per-capita GDP in their respective countries.
In general, the countries that perform well are those who attract the best students into the teaching profession by offering them higher salaries and greater professional status. School systems that invest in teachers' salaries tend to have larger classes - but at country level, Pisa finds that the size of the class is unrelated to overall performance.
Another common factor in success is high expectations for all of their students.
"Schools and teachers in these systems do not allow struggling students to fail; they do not make them repeat a grade, they do not transfer them to other schools, nor do they group students into different classes based on ability," states the latest Pisa in Focus report.
"Regardless of a country's or economy's wealth, school systems that commit themselves, both in resources and in policies, to ensuring that all students succeed perform better in Pisa than systems that tend to separate out poor performers or students with behavioural problems or special needs."