Studies on school achievement and social justice

International studies on school achievement claim to record relevant learning results in the school systems of the countries participating in order to provide quality indicators for descriptive and analytic comparisons. Thus, the question arises whether the methods of pedagogical diagnosis employed here suffice to allow for similar research conditions which are at the same time sufficiently sensitive regarding the national peculiarities of the educational systems. This issue may be summarized in the concept of fairness. From the school-pedagogical point of view, fairness aims at the question of social justice within the institution 'school'. In the field of psychological diagnosis and in that of test theory, in particular, fairness represents an instrumental value criterion or, rather, the result of an adequate test quality. Taking TIMSS (Third International Mathematics and Science Study) as an example, the author shows that, with the methods of advanced pedagogical-psychological diagnosis, a high degree of fairness may be achieved in international comparative research on school achievement.