Teacher education programs have met with limited success in improving teachers' understanding of the nature of science (NOS). Research suggests that such efforts could be enhanced by addressing NOS in preservice teachers' science courses. We planned NOS instruction in a physical science content course for preservice elementary teachers. Our first concern was the NOS views of the instructors for the course, which included undergraduate teaching assistants (UTAs). We examined the NOS views of nine UTAs, and the impact of job-embedded professional development on their views. Although initially UTAs held a number of views inconsistent with science education reforms, four modes of explicit-and-reflective interventions, including analysis of NOS views of preservice teachers, resulted in favorable changes in UTAs' views.