'Literacy in the Science Classroom Project" was a three-year professional development (PD) program supporting minority-language secondary teachers' use of effective language-based instructional strategies for teaching science. Our primary objective was to determine how teacher beliefs and practices changed over time and how these were enacted in different classrooms. We also wanted to identify the challenges and enablers to implementing these literacy strategies and practices at the classroom, school, and district levels. Data collection involved both qualitative and quantitative methodologies: student questionnaires; interviews with teachers, principals, and mentor; and focus groups with students. The findings suggest that the program had an impact on beliefs and practices commensurate with the workshop participation of individual teachers. These language-enhanced teacher practices also had a positive impact on the use of talking, reading and writing by students in the science classroom. Finally, continuing PD support may be needed in certain jurisdictions for strengthening minority-language programs given the high teacher mobility in content-area classrooms evident in this study.