The purpose of this mixed-methods study was to examine the impact of a long-term, 5E inquiry-based professional development on content and pedagogical knowledge in eighth-grade science teachers in Texas. Qualitative and quantitative data were collected via university designed reflective prompts, science content pretests and post-tests, and a classroom observation instrument. Results showed the professional development had a statistically significant impact on teachers' content knowledge in earth science, less significant impact in content knowledge in physical science and that teachers' levels of inquiry-based practice were in the early stages. The teachers' reflections of the professional development's impact indicated self-identified growth in their content knowledge and an impact on their understanding of inquiry-based classroom instructional practice. The findings suggest inquiry-based professional development has an impact on teachers' content and pedagogical knowledge, specifically regarding conveying content effectively, concept interconnection, lesson design, and teachers' opportunities to experience inquiry-based learning themselves before implementing it in their classrooms. The study's implications for further research include examinations of professional learning opportunities at local district and campus levels to identify and incorporate science teachers' existing levels of content and inquiry-based pedagogical knowledge and provide opportunities for practice to incorporate the pedagogy in classrooms.