The No Child Left Behind Act requires that all teachers be certified within the content areas that they teach. However, attracting and retaining highly qualified science teachers in rural school districts is particularly difficult due to limited resources and geographic and professional isolation. Science professional development programs could help improve inservice teachers' understanding of concepts they are expected to teach, but such programs are often limited in rural areas. This study evaluates a unique distance learning, inquiry-based professional development course in physical science developed to meet the needs of central Appalachian middle school teachers. Instruction through hands-on inquiry investigations distinguishes this program from other distance learning programs. Preliminary findings from the pilot study reported in this paper reveal significant growth in 43 teachers' content knowledge for six of nine temperature and heat concepts assessed in the course. Outcomes from the distance learning project are discussed as they relate to future research goals and implications for science professional development programs in rural regions.