The OECD (Organisation for Economic Co-operation and Development) has published a new PISA in Focus review analyzing the results of their PISA (Program for International Student Assessment) study. It explores whether money "buys" improved performance for a country, and finds that higher expenditure on education does not guarantee better student performance. National wealth is important up to a point, and this research focuses on countries above a certain baseline. But, for relatively high-income economies, the success of the country's education system depends more on how educational resources are invested, than on the volume of investment. Investing in teachers and having high expectations for all students are cited as particularly important characteristics.