The present article gives an overview of several studies on the predictive validity of the Ctest. In the first part of the article, we discuss the construct validity of this test format. Only if
the underlying construct of this test is understood, can a justification for high predictive
validity be made. In the second part, we discuss several previous studies where the C-test
format is used to predict the study and training success of international students. The third
part discusses the findings of two as yet unpublished studies on the predictive validity of the
C-test. We wish to contribute to the ongoing discussion of the validity of the C-test and argue
that it is not only a language test, but also a test of processing speed which is related to
working memory. For international students, processing speed in English as a foreign
language is related to vocabulary knowledge, which includes statistical knowledge about the
probability of words occurring in a given context as well as the probability of words
following or preceding each other. The C-test taps precisely into these aspects of language
proficiency which explains its high predictive validity for the study success of international
students.