This paper uses extensive student-level micro databases of three international student achievement tests to estimate heterogeneity in the effect of external exit exams on student performance along three dimensions. First, quantile regressions show that the effect tends to increase with student ability. But it does not differ substantially for most measured familybackground characteristics. Second, central exams have complementary effects to school autonomy. Third, the effect of central exit exams increases during the course of secondary education, and regular standardised examination exerts additional positive effects. Thus, there is substantial heterogeneity in the central exam effect along student, school and time dimensions.