Purpose: Collective efficacy (CE)--a group's belief in its capabilities to organize and execute courses of action required to reach a goal--is an important organizational property because it facilitates goal attainment. The purpose of this sequential explanatory mixed-methods study was: (1) to affirm the link between CE and student achievement; (2) to understand the antecedents of CE; and (3) to illustrate how school leaders shape conditions to promote CE. Research Methods/Approach: Using statewide data drawn from a stratified random sample of schools, analyses were conducted utilizing hierarchical generalized linear modeling. To probe the relationship between CE and student achievement, two high-poverty schools, differentiated by levels of CE and student performance, were selected for case studies. Findings: Quantitative results confirm CE was related to fourth-grade students' odds of passing state standardized assessments in reading and mathematics. Case studies revealed principals created structures that enhanced instructional program coherence, which may have enriched CE. Implications: These findings underscore the importance in leadership in supporting CE. Specifically, leaders foster the conditions to enact an instructional framework that serves as an opportunity to not only build CE but also articulate CE beliefs.