Purpose: The purpose of this study was to examine how principal support, professional learning communities, collective responsibility, and group-level teacher expectations affect 11th-grade student math achievement. Research Methods: Data for this study were from the High School Longitudinal Study of 2009, administered by the U.S. Department of Education, National Center for Education Statistics. This study used a multilevel structural equation model to examine how principal support, professional learning communities, collective responsibility, and teacher expectations at the group level affect school math achievement. Findings: The study identified a model of school-level factors affecting students: Principal support positively influenced both professional learning communities and collective responsibility, which in turn, affected student math achievement via group-level teacher expectations; on the other hand, the impact of principal support on group-level teacher expectation and the direct associations of both professional learning communities and collective responsibility with student achievement were not statically significant. Implications: Focusing on how a school-level mechanism influences student achievement provides a better understanding of sustaining high school performance through school reform initiatives (e.g., principal leadership training, building professional learning communities, or interventions to improve group-level teachers' expectations). To improve student achievement, the current study emphasizes why principals should give more attention to exerting supportive and egalitarian leadership that can contribute to a school's positive climate and lead to changing teachers' instructional behaviors and attitudes, rather than focusing on directive or restrictive leadership and managing behaviors.