This study explores the principal's role as instructional leader in four urban schools showing improvement in test scores. Data gathering procedures included ethnographic observations and interviews of principals; principals' logs of time use; interviews with teachers, school administrators, and students; and faculty surveys. The findings were analyzed to identify "cultural themes" dealing with instructional leadership and to develop composite pictures of the principals' leadership. The bulk of the report consists of case studies incorporating anecdotal and quantitative presentations of such topics as the community, characteristics of the school, composition of students and faculty, a profile of the principal, the principal's exercise of instructional leadership, faculty and student perceptions, the principal's interventions for instructional improvement and their effects, and the school's leadership structure, including the role of other influential staff. General findings indicate that principals can improve learning by establishing explicit policies for achieving clearly expressed goals, effectively using slogans in support of those goals, improving the learning climate, and having someone devote attention to the curriculum. The conclusion is that the principals studied give priority to student discipline and school management and need inservice education to become instructional leaders. Principals can provide general instructional leadership while support staff with special expertise offer more specific leadership. (Survey instruments including Sources of Instructional Leadership (SOIL) are appended.) (MJL)