We examine whether teachers' communicator style relates to student engagement, teacher-student relationships, student perceptions of teacher immediacy, as well as observer ratings of delivery skills during the implementation of All Stars, a middle school-based substance use prevention program. Data from 48 teachers who taught All Stars up to 3 consecutive years and their respective seventh-grade students (n = 2,240) indicate that having an authoritative communication style is negatively related to student engagement with the curriculum and the quality of the student-teacher relationship, while having an expressive communicator style improves teachers' immediacy to student needs. Adaptations made by a subsample of teachers (n = 27) reveal that those who were more expressive asked students more questions, used more motivational techniques, and introduced more new concepts than authoritarian teachers.