Vocabulary knowledge is vital for students' success in school and beyond. However, students with disabilities and others who consistently score below their peers on various measures of vocabulary knowledge have difficulties in secondary-level content area courses. Because many students with disabilities are now educated primarily in general education classrooms, their teachers report needing more professional development on instructional strategies to support this population. Using a multiple-baseline design, we tested the efficacy of a multimedia, multicomponent professional development package in which middle school science teachers in inclusive classrooms promoted science vocabulary knowledge. The professional development package improved the quality of the teachers' use of evidence-based vocabulary practices and increased the amount of time they spent explicitly teaching vocabulary in their classes.