School administrators' uses of subjective understandings and common language to gain and maintain power and predictability in their environments are described. Micropolitical theory, with a focus on language, is utilized to understand administrators' knowledge of the assumptive worlds of their subculture, and how these assumptive worlds constrain and limit conflict. Interviews with 20 assistant principals and onsite observations of their schools identified four domains of site-level assumptive worlds: (1) the right and responsibility to initiate; (2) acceptable and unacceptable values; (3) patterns of unexpected and sanctionable behavior; and (4) special conditions management. Assumptive worlds create in administrators the following characteristics: avoidance of value conflict and risky change, defensiveness, and belief in a "one best system." A conclusion is that assumptive worlds function to reduce inherent dilemmas by confining values and behaviors to acceptable domains. An implication is that reform efforts and administrator education programs will encounter administrator resistance when mandated in ways that disrupt assumptive worlds and must therefore consider political behavior. A table that lists assistant principals' policy initiatives is included. (26 references) (LMI)