The purpose of this study was to examine the conceptualization, measure and impacts of school principals' sense of efficacy for instructional improvement. Based on social cognitive theory and prior research, we hypothesized that principals' sense of efficacy for instructional leadership would directly predict teachers' collective efficacy beliefs and indirectly predict student achievement through collective efficacy. We employed multilevel structural equation modeling (MSEM) to analyze data collected from 95 principals, 1,623 teachers, and 4,229 students in a Midwestern state. Results indicated that principals' efficacy beliefs positively and significantly predicted teachers' collective efficacy beliefs, which in turn predicted student achievement.