Based on data gatered from interviews, observations, and document reviews during a 3-year qualitative examination of curriculum change projects in 14 elementary, junior, and senior high schools, this paper argues that the spread of new classroom practices within a school beyond a core committee of planners is determined by the orgaanizational structure of the school's four types of subunits, which are defined by the nature of the linkages they exhibit: "the social club" (characterized by congeniality, horizontal linkages, and much informal interaction among teachers about instructional matters); "the professional group" (horizontally linked but more formal in its adherence to written guidelines); "the administrator's delight" (vertically linked and willing to follow an administrator's directives); and "the egg crate" (loosely linked both horizontally and vertically and involving teachers who work in isolation, rarely discussing instruction). The paper first defines the concepts of organizational linkages, change implementation, and field agent strategies. Next, research procedures and background information are provided. Finally, the paper describes how different change strategies were appropriate or inappropriate in each subunit. Two tables provide data on the schools involved in the study and the quantity of implementation in the planning groups and in the schools as a whole. (PB)