Researchers using a combination of principal logs, on-site observation, face-to-face interviews, and regularly scheduled telephone interviews documented how principals intervene in the management of school change on both a day-to-day and a year-long basis. The data are from the Principal-Teacher Interaction Study conducted at the Austin campus of the University of Texas. Two analytical frameworks, a "taxonomy of interventions" and an "anatomy of interventions," were used to structure the data collection and to analyze the behavior of the principals. The taxonomy of interventions involves the identification of levels of interventions. This paper focuses on the analysis of "incident" interventions, the smallest intervention unit. The anatomy of interventions involves the examination of each individual incident-level intervention in terms of its internal parts. Findings reported are from studies of three California school principals in their first year of implementing a writing composition program, and of three Florida principals in their second year of the implementation of a mathematics curriculum. Frequencies of the targets, functions, medium, and flow of the principals' interventions are presented and discussed. One of the important findings of the study is that support and facilitation for teachers continued throughout the second year of implementation with little decrease in activity by the principals. (Author/MLF)