  At large research universities in the USA, introductory physics labs are
often run by graduate student teaching assistants (TAs). Thus, efforts to
reform introductory labs should address the need for effective and relevant TA
professional development. We developed and implemented a research-based
professional development program that focuses on preparing TAs to effectively
support inquiry-based learning in the lab. We identify positive effects by
examining three possible ways in which the professional development might have
impacted TAs and their work. First, we examine lab TAs' written reflections to
understand the effect of the program on TAs' ways of thinking about student
learning. Second, we observe and categorize TA-student interactions in the lab
in order to investigate whether TA behaviors are changing after the
professional development. Third, we examine students' attitudes toward
experimental science and present one example case in which students' attitudes
improve for those TAs who `buy in' to the professional development. Our results
suggest lab TA professional development may have a tangible positive impact on
TA performance and student learning.
