A goal in many countries is to institute state-wide exams to base student assessment more firmly on norms for all classes. This raises the question as to the extent to which greater standardization of grading practice can be reached by implementing state-wide exit exams. Since there is a lack of longitudinal studies, we analyzed the effect of the implementation of state-wide exit exams in all 19 academic upper secondary schools (N = 19) in the German state of Bremen over 5 years. We used a standardized achievement test in mathematics and students' exit exam and semester grades. For the advanced courses, the results show a standardization effect at the school level and for semester grades. No standardization effect is found for the exit exams on the individual level. For the basic courses, the results show positive effects for semester and exit exams grades. Theoretical and practical implications as well as the robustness of the findings are discussed.