In the project MoKoM, which is funded by the German Research Foundation (DFG) from 2008 to 2012, a test instrument measuring students’ competences in computer science was developed. This paper presents the results of an expert rating of the levels of students’ competences done for the items of the instrument. At first we will describe the difficulty-relevant features that were used for the evaluation. These were deduced from computer science, psychological and didactical findings and resources. Potentials and desiderata of this research method are discussed further on. Finally we will present our conclusions on the results and give an outlook on further steps.