The fourth volume of a 10-volume report, this document provides a synthesis and analysis of indepth ethnographic case studies of 12 school districts engaged in school improvement efforts in a subsample of the study's 146 districts. All districts were implementing new practices, seven using National Diffusion Network innovations and five developing and implementing practices of their own design funded through Title IV-C Development Grants. Each stage of the implementation process is portrayed, from preadoption to institutionalization, when it occurred. The motivations, behaviors, and aspirations of school personnel involved in the improvement effort are explored; aspects of the implementation process, including factors affecting its success, are examined; and outcomes, including impact on students, are discussed. Four patterns leading to the success or failure of implementation are identified: "enforced, stabilized use,""overreaching,""blunting/downsizing," and "indifference/discouragement." (TE)