AAAS (American Association for the Advancement of Science) is collaborating with BSCS (Biological Sciences Curriculum Study) in the development of a curriculum unit for eighth grade students that connects fundamental chemistry and biology concepts to better prepare them for high school biology. Recognizing that teachers play an influential role in delivering the curriculum to students, we developed teacher support materials and professional development designed to help teachers use the unit effectively. In order to learn about the promise of the teacher support materials, we developed an assessment targeting aspects of participating teachers' (n = 8) science content knowledge and pedagogical content knowledge (PCK) for the specific learning goals of the unit. Specifically, the assessment targeted three areas of teachers' knowledge: 1) content knowledge 2) knowledge of student thinking, and 3) knowledge of strategies to move student thinking forward, across four item contexts: 1) chemical reactions, 2) conservation of mass, 3) flow of matter in living systems, and 4) plant growth. Teachers took the assessment three times: before PD, after PD, and after teaching the unit. The assessment items were mainly constructed response and were scored using indicators of success and difficulty. Teachers made gains over time in most of the knowledge areas and across most of the contexts. Areas where they did not make clear progress, or where their knowledge was particularly low, indicated that either the assessment instrument or the teacher support materials could be improved. Revisions based on these findings are reported. (Contains 4 tables and 1 figure.)