Within the interdisciplinary research project 'Measurement Procedure for Informatics in Secondary Education (MoKoM)”, conducted at the Universities of Paderborn and Siegen with help from Peter Hubwieser, Technical University of Munich, researchers aimed to develop a theoretically and empirically sound competence model for the domains of system comprehension and system modelling, alongside an evaluated measurement instrument to assess competences of students in upper secondary computer science education in German schools. The competence model was thoroughly developed by conducting several theoretical and empirical steps. Based on the model measurement items were constructed and compiled into an instrument with 87 items of varying complexity. The instrument was divided into six booklets and distributed to over 800 computer science students in three German states. The returned 583 tests were analysed by means of the multidimensional item response theory, to assess the item difficulty on the one hand and the student abilities on the other. The results are used in several ways: to evaluate the competence model, to revise the measurement instrument and to define proficiency levels in a competence level model by using the method of scale anchoring.