The single greatest determinant of student learning is the faculty. Teachers are far more important than the curriculum, facilities, administration or any other aspect of a school’s operations. Investment in teachers yields a high rate of return, improves teaching and learning, and helps to improve schools.Central to determining teacher effectiveness is faculty culture. A healthy faculty culture is essential for students to learn and teachers to teach at the highest levels of their abilities. On the flip side, an unhealthy culture is a disease that permeates the life of the school community and saps energy for learning.We know that school culture and the nature of relationships among adults in schools is a significant determinant of students’ academic and social progress. While subject-area knowledge and teaching skills are necessary, a school’s faculty culture, more than any other factor, determines the level of student learning. Yet, faculties are typically characterized by departmentalization, turf wars and isolation. As Roland Barth states so well, “All too often, the adult relationships are (in that wonderful phrase from preschool education) parallel play. For hours at a time, two- and three-year-olds in a sandbox can be so engrossed in themselves, in their own work and project and tools, that they are oblivious to anybody else in the sandbox. This is thought to be a stage of development through which two- and three-year-olds soon pass on their way to far more sophisticated forms of human interaction. But I’d say that parallel play characterizes most of what I see going on in schools. The self-contained classroom is parallel play. The English department that doesn’t interact with the math department is parallel play. One school doing one thing, the school a mile down the road doing something different, oblivious to each other, is parallel play. Parallel play is endemic. It’s as if we have a case of professional arrested development.” Unfortunately, Barth is correct. Fortunately, schools that invest in developing and maintaining a healthy faculty culture significantly improve student learning, create a dynamic and engaging learning community and establish a competitive edge in the marketplace.Although schools must ultimately define healthy faculty culture for themselves, traits such as collegiality, trust, validation, creativity, recognition, innovation and humility contribute to creating and sustaining a healthy faculty culture. Conversely, cynicism, suspicion, defensiveness, poor communication and isolation are examples of traits that create an unhealthy culture. A culture characterized by enthusiastic commitment to learning and personal growth, collaboration, and unremitting devotion to each and every student’s success is essential for student learning to thrive. We need to elevate learning at all levels above all other concerns, activities and goals, and value dearly experimentation, new ideas, adventure and discovery. Teachers must teach teachers, observe each other, give constructive feedback, and collaborate across disciplines. Learning is at its best in a school culture, created by adults and students, which values leaning above all else. In fact, research clearly demonstrates that student learning correlates directly to adult learning. Assessing, analyzing and improving faculty culture is all about learning together as a faculty and staff.School improvement and the process of defining and building a healthy faculty culture involve both administrators and teachers. The first step is to assess the existing culture. Several assessment tools are available. The Faculty Culture Profile is one good example. The second step is to analyze the information and develop an action plan to address the issues and improve faculty culture. Total faculty involvement and strong leadership from the school’s head and other administrators are essential. The analysis of the results of the assessment will likely surface some difficult issues. Dealing with these issues openly, honestly and respectfully is critical to school improvement and to building a healthy faculty culture. The process of addressing the problems must be forward looking and solution oriented.