Purpose: The leadership of the principal is known to be a key factor in supporting student achievement, but how that leadership is experienced and instructionally enacted by teachers is much less clear. The purpose of this study was to examine various factors that are often present in principal-teacher interactions and teacher-teacher relationships to see how those may have an impact on teachers' classroom instructional practices. Data Collection and Analysis: Data for this quantitative study are from a teacher survey developed for the national research project, Learning from Leadership, funded by the Wallace Foundation. There are 4,165 completed surveys in the database, which reflects responses from teachers in grades K-12 in a sample of schools across the United States. Using a conceptual framework based on various known components of effective schools today, a stepwise linear regression examined the relationships among practices such as shared leadership and professional community with contextual variables such as trust and efficacy. Findings: Three types of instructional behaviors--Standard Contemporary Practice, Focused Instruction, and Flexible Grouping Practices--emerged as strong factors which operationally described effective teacher practice. The presence of shared leadership and professional community explain much of the strength among the three instructional variables. Furthermore, the effect of teachers' trust in the principal becomes less important when shared leadership and professional community are present. Self-efficacy strongly predicts Focused Instruction, but it has less predictive value for the other measures of instructional behavior. Individual teacher characteristics of gender and years of experience have clear impact on instructional practice, but there are no discernible patterns that suggest that the level of the principal (elementary vs. secondary) have more or less influence on teacher instructional behaviors. Conclusions: Increasing our knowledge about what leaders do and how they have an impact on the instructional behaviors of teachers will lead us to a better understanding of how leadership has a direct relationship to improved student achievement. These findings create a clearer picture of teacher-principal and teacher-teacher interactions that support learning and bring us closer to the elusive goal of clarifying the link between leadership and learning. (Contains 1 figure, 6 tables, and 3 notes.)