This article investigates the participating students' evaluation of a teacher training seminar about heterogeneity in the classroom at Bielefeld University, Germany. The evaluation made use of a short questionnaire and an end-of-term test of the students' knowledge on the subject matter. The questionnaire is tested for objectivity, reliability, and validity and is shown to be a suitable tool. The test is shown to have certain weaknesses, but ways of improving it for future use are suggested. The method of evaluation used in this study can be adapted for other university courses. The importance of using empirical methods such as the one employed in this study for the improvement of teacher training is stressed. The seminar in question is shown to be largely successful and to contribute to the development of central diagnostic skills defined by the German conference of ministers of education.