  Instruction is unlikely to be effective if instructors do not know the common
alternate conceptions of introductory physics students and explicitly take into
account common student difficulties in their instructional design. Here, we
discuss research involving the Conceptual Survey of Electricity and Magnetism
(CSEM) to evaluate one aspect of the pedagogical content knowledge of teaching
assistants (TAs): knowledge of introductory students' alternate conceptions in
electricity and magnetism as revealed by the CSEM. For each item on the CSEM,
the TAs were asked to identify the most common incorrect answer choice selected
by introductory physics students if they did not know the correct answer after
traditional instruction. Then, we used introductory student CSEM post-test data
to assess the extent to which TAs were able to identify the most common
alternate conception of introductory students in each question on the CSEM. We
find that the TAs were thoughtful when attempting to identify common student
difficulties and they enjoyed learning about student difficulties this way.
However, they struggled to identify many common difficulties of introductory
students that persist after traditional instruction. We discuss specific
alternate conceptions that persist after traditional instruction, the extent to
which TAs were able to identify them, and results from think-aloud interviews
with TAs which provided valuable information regarding why the TAs sometimes
selected certain alternate conceptions as the most common but were instead very
rare among introductory students. We also discuss how tasks such as the one
used in this study can be used in professional development programs to engender
productive discussions about the importance of being knowledgeable about
student alternate conceptions in order to help students learn.
