Because public school districts have highly permeable organizational boundaries, analyses of their structures and processes should include consideration of external as well as internal factors. Such analyses have become feasible with the application of general systems theory, which views organizations as functioning units that have continuous interaction across boundaries. The recent application of general systems theory to organizational structures by Pfeffer and Salancik contends that external factors, such as population mobility, external mandates, and religious and cultural conditions, are influential in both the public and private sectors. Two case studies of executive succession in public schools--one in an urban-rural district using a centralized, districtwide approach to linking testing and evaluation activities with district instructional programs, the other in a large urban district using a decentralized, school-by-school approach--confirm Pfeffer and Salancik's model of environmental effects. In both cases, the selection of superintendents reflected the environmental context, which in turn influenced district power distribution. Findings confirmed Pfeffer and Salancik's perception that external environmental influences exert control on the internal workings of an organization. School administrators should understand such external conditions to attain optimal organizational effectiveness. (JBM)