The assessment of mathematical competence for ninth graders in the National Educational Panel Study (NEPS-K9) and the German National Assessment at the end of secondary education (LV) show a large conceptual overlap. To examine the possibility of transferring the LV performance standards to the test scores of the NEPS-K9, a linking study was set up with N = 636 students which examined mathematics items from both tests in a single group design. The NEPS test scores were linked to the LV test with the equipercentile method. The distributions of the scores in both the LV and NEPS test as well as the distribution that resulted out of the linking were compared. Furthermore, the robustness of the linking was analysed by subgroup and classification consistency. The linking produced similar distributions of scores and performance standards but differed significantly for the individual classifications. Thus, inferences are possible on a population level, but the results should not be interpreted on an individual level.