The design of PISA does not just allow for a comparison of the relative standing of countries in terms of their learning outcomes; it also enables each country to monitor changes in those outcomes over time. Such changes indicate how successful education systems have been in developing the knowledge and skills of 15-year-olds. Indeed, some countries have seen impressive improvements in performance over the past decade, in some cases exceeding the equivalent of an average school year’s progress for the entire student population. Some of these countries have been catching up from comparatively low performance levels while others have been advancing further from already high performance levels. All countries seeking to improve their results can draw encouragement — and learn lessons — from those that have succeeded in doing so in a relatively short period of time.