A report is given on the second phase of a 3-year study on change in American high schools. Data are presented from 17 schools for two of the study questions: What types of changes are occurring and what are the key units of change? Information was collected through approximately 28 hours of interviews in each school with students, faculty, and administrators. Additionally, the kinds of changes being proposed in some of the major national and state commission reports were analyzed and compared with the changes underway in the study schools. The changes identified in the study were divided into three categories: schoolwide, subunits, and individual. The kinds of changes being made involved: (1) changes related to regularly scheduled curriculum or instruction; (2) changes in school-sponsored activities that are not a part of regularly scheduled curriculum; (3) changes directed at school personnel; (4) administrative changes; (5) changes in school facilities; and (6) changes in school relations with external groups. Data from findings in each of these areas are presented in tables. Findings indicate that major changes are not being made in the structure or organization of the schools, or in the processes of schooling. A majority of changes were directed specifically to improving student achievement. (JD)