This study reports on the findings of a qualitative research case study designed to evaluate the effectiveness of a professional development program on teaching disciplinary literacy through historical inquiry. Thirteen secondary social studies and English teachers participated throughout one academic school year. Participants were evaluated for their implementation of historical inquiries using primary sources and engaging students in disciplinary literacy practices using observations of classroom instruction and self-reporting surveys. The results indicated a positive relationship between teacher participation in the professional (...) development and improvement in inquiry-based instructional approaches, incorporation of disciplinary literacy practices, and increases in their use of primary sources in the classroom. Social validation indicated that teachers found the program beneficial. This study contributes to the body of knowledge focused on disciplinary literacy and historical inquiry. (shrink)