This paper considers the kinds of interventions that elementary school principals make for the purpose of improving practice in their schools. Findings are derived from the Principal-Teacher Interaction Study being conducted at the University of Texas at Austin, which has categorized interventions hierarchically at the following levels: policy, game plan, strategy, tactic, and incident. This paper presents only the results of the first data analysis of incident-level interventions from this study. After a review of the literature and a description of the Principal-Teacher Interaction Study, its taxonomy of interventions, and its schema for anatomizing each intervention, data are reported regarding frequency of interventions during the 2 years of the study, the targets of principals' interventions, their function, medium, and "flow" (i.e., interactive or one-way). The subsequent section presents 10 generalizations about the modus operandi of principals, followed by a case-by-case description of several exemplary types of intervention and their effects on teachers. A discussion of implications follows, along with an appendix describing the three change-facilitator styles (responders, managers, and initiators) and three pages of references. (TE)