Belgium occupies a distinct position in PISA 2012 scores. First, the Belgian educational system belongs to the international top in terms of performance. The top students in Belgium score second highest of all ISCY countries on mathematics. However, Belgian 15-year olds are also among the worst performing students on these tests, scoring only slightly better than students from France, Iceland, Norway, Spain, and USA. No wonder then, that Belgium has the highest level of inequality in achievement of all countries taking part in the ISCY-study, as shown by the spread on the PISA results. The aim of the current paper is to offer explanations for this peculiar position of Flanders by searching for system influences on student performance. First, we will discuss the specificities of the Flemish educational system. Thereafter, we will argue that the Flemish tracking system is one of the most important reasons for the existence of the large performance gap.