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Exploring Pedagogical Content Knowledge of Physics Instructors and Teaching Assistants Using the Force Concept Inventory

The Force Concept Inventory (FCI) has been widely used to assess student understanding of introductory mechanics concepts by a variety of educators and physics education researchers. One reason for this extensive use is that many of the items on the FCI have strong distractor choices that correspond to students' alternate conceptions in mechanics. Instruction is unlikely to be effective if instructors do not know the common alternate conceptions of introductory physics students and explicitly take into account students' initial knowledge state in their instructional design. Here, we discuss research involving the FCI to evaluate the pedagogical content knowledge of both instructors and teaching assistants (TAs) of varying teaching experience. For each item on the FCI, the instructors and TAs were asked to identify the most common incorrect answer choice of introductory physics students. We also discussed the responses individually with a few instructors. Then, we used the FCI pre-test and post-test data from a large population (~900) of introductory physics students to assess the pedagogical content knowledge of physics instructors and TAs. We find that while both physics instructors and TAs, on average, performed better than random guessing at identifying introductory students' difficulties with FCI content, they did not identify many common difficulties that introductory physics students have, even after traditional instruction. Moreover, the ability to correctly identify students' difficulties was not correlated with the teaching experience of the physics instructors.