A study involving random assignment of all youth eligible for Job Corps to either a Job Corps program or to a control group was conducted to assess the impact of Job Corps on key participant outcomes. Participants in the study were nationwide youth eligible for Job Corps who applied for enrollment for the first time between November 16, 1994, and December 17, 1995. The study sought to determine the following:(1) how effectively Job Corps improves the employability of disadvantaged participants, (2) whether Job Corps impacts differ for youths with different baseline characteristics, and (3) how effective the residential and nonresidential components of Job Corp are. Findings over the first 4 years after random assignment include the following: (1) Job Corps provided extensive education, training, and other services to the program group and improved their educational attainment; (2) Job Corps generated positive employment and earnings impacts by the beginning of the third year after random assignment and the impacts persisted through the fourth year; (3) employment and earnings gains were found broadly across most subgroups of students; (4) the resident and nonresidential programs were each effective for the youths they served; (5) Job Corps significantly reduced youths' involvement with the criminal justice system; (6) Job Corps had small beneficial impacts on the receipt of public assistance and self-assessed health status, but no impacts on illegal drug use; and (7) Job Corps had no impacts on fertility or custodial responsibility, but it slightly promoted independent living and mobility. (The report include numerous tables and charts, 31 references, and five appendixes concerning the study methodology.) (KC)