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