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The relative age effect ( rae) refers to the performance-related advantage of being born early in a cohort. In education economics, the rae shows that children born early in the year obtain better results than their peers. This is also true in sports education in which children are grouped by age during their training period. The main explanation of rae is the cutoff dates in youth sport. Because the cut-off date never changes, it is particularly difficult in education economics to identify the causal effect of the cut-off date on rae. On the other hand, sports and in particular soccer provides cases where the cut-off date in youth school changed : The French Football Association changed the cut-off date from during the 1995-1996 season. We show (1) the rae is caused by a change in the cut-off date ; (2) the rae still exists for older players (3) football players born in the fourth quarter have a physical superiority measured by the body mass index ( bmi). Codes JEL : L83 ; C90