Recently, the Faculty of Political Science at the University of Bologna has started a program of didactics reorganization for several courses, introducing more than one evaluation test during the learning process. Student assessment before the final examination has the double aim of measuring both the level of student’s ability and the effectiveness of the teaching process, in order to correct it real-time. In such an evaluation system, common to the Anglo-Saxon countries, Item Response Theory (IRT) expresses its effectiveness fully. In this paper, an IRT model for ordered polytomous variables is considered in order to investigate the item properties and to evaluate the student achievement. Particularly, the Graded Response Model (GRM) is taken into account in the analysis of three different written tests of a basic Statistics course. The results highlight the different composition of the items and provide a simple description of the student ability distribution.
