Current reforms in the education policy of various countries are intended to produce a paradigm shift in the educational system towards an outcome orientation. After implementing educational standards as normative objectives, the development of test procedures that adequately reflect these targets and standards is a central problem. This paper constructs the theoretical framework for the assessment of students' content knowledge in chemistry. The resulting scheme and manual were used to develop model-based tasks in various content areas. Students' performances in paper and pencil tests taken in school grades 6 to 12 were analyzed. The quantitative data were used for a reliable classification of the tasks. The results shed light on the development of content knowledge in chemistry as well as on the various systematic factors that influence students' performance. (Contains 6 tables and 2 figures.)