Pedagogical content knowledge (PCK) and content knowledge (CK) are important dimensions of teachers' professional knowledge that are addressed in education programs for science teachers. In this article we present the structure, content, and evaluation of a preservice biology teachers' training program (N=173) to develop an elaborate understanding of models and modeling for scientific inquiry. Teachers need a profound understanding of this content as well as knowledge how to teach their students in this field. This implemented teachers training program uses the case method to foster both: knowledge concerning models and modeling as part of CK (as precondition) and content-related diagnostic and teaching knowledge as part of PCK. The effect of the program on the preservice biology teachers' knowledge in both areas was evaluated with a pre-post-experimental-control group design using open-ended items for the assessment of model competence and semi-open-ended items and test cases, assessing both diagnostic and teaching knowledge. The quantitative analyses of the open-ended items reveal a significant positive development of model competence from pre- to post-assessment. The qualitative analyses of the test case data reveal a positive development of diagnostic and teaching knowledge (PCK) in the experimental group. Thus, these results give some evidence for using the case method in preservice biology teacher training programs.