The OECD's Programme for International Student Assessment (PISA) is gaining increasing attention among education authorities of the world. The number of participating economies almost doubled in the past one and a half decades, increasing from 43 in 2000 when it first started to 74 in 2015. PISA assesses the performance in Reading, Mathematics, and Science of 15-year-olds with different emphases rotating among the three subjects in different exercises. The attention of the participating economies has been focused almost exclusively on the ranking results which are used to evaluate the standings and progress of their education systems, although PISA does cover many background conditions which might have influenced the performance. Interestingly, East Asian economies have been consistently in the leading positions, and Finland has been frequently cited as a model for the Western economies and even the world to emulate. This monograph contains many secondary analyses of PISA data. It presents results of comparisons of Singapore, East Asian economies, and the world. It also points up some influencing factors such as time in and after school, test-language effect, administrative styles, and school environment. Statistical and measurement issues are also raised and demonstrated. Moreover, cultural differences are evoked as a plausible explanation of the differences observed between the East and the West. This monograph, using mainly simple and layman language, equips educational administrators and policy makers with in-depth insights into some of the intricacies inherent in the PISA data for a more appropriate understanding. It is readily appreciated that such an understanding is needed to prevent misinterpretation and avoid unsound policy or wasteful action.