The Job Corps program has long been a central part of federal efforts to provide training for disadvantaged youths. Because of the high costs of the program's intensive services, which are provided mainly in a residential setting, policymakers need to know just how effective Job Corps actually is. This report presents the findings of the National Job Corps Study on impacts of the program on participants' employment and related outcomes. The cornerstone of the National Job Corps Study was the random assignment of all youths found eligible for Job Corps to either a program group or a control group. Program group members could enroll in Job Corps; control group members could not, but they could enroll in all other programs available to them in their communities. We estimated impacts by using data from periodic follow-up interviews to compare the experiences of the program and control groups. Findings on program impacts over the first four years after random assignment are summarized below. Job Corps provided extensive education, training, and other services to the program group. Follow-up interviews show that 73 percent of the program group enrolled in Job Corps, with an average period of participation of eight months. Students received large amounts of academic classroom instruction and vocational skills training. They also participated extensively in the primary Job Corps activities outside the classroom. Job Corps substantially increased the education and training services that eligible applicants received, and it improved their educational attainment. On average, Job Corps increased participants¿ time spent in education and training (both in and out of Job Corps) by about 1,000 hours, approximately the number in a regular 10-month school year.