Making the successful transition to adulthood has become increasingly difficult for many young people in the United States, particularly for those without a college education. Those without a high school degree face even tougher prospects, with especially high unemployment rates and falling wages. A typical worker without a high school diploma earns less today than the same worker did in the 1970s. YouthBuild is a program that attempts to improve prospects for less-educated young people, serving over 10,000 individuals each year at over 250 organizations nationwide. Each organization provides hands-on, construction-related or other vocational training, educational services, case management, counseling, service to the community, and leadership-development opportunities, to low-income young people ages 16 to 24 who did not complete high school. YouthBuild was evaluated using a randomized controlled trial, in which eligible young people at participating programs were assigned to either a program group, invited to enroll in YouthBuild, or a control group, referred to other services in the community. The evaluation included 75 programs across the country and nearly 4,000 young people who enrolled in the study between 2011 and 2013. This report, the final in the evaluation, presents the program's effects on young people after four years. Main findings observed through four years indicate that the program provides a starting point for redirecting otherwise disconnected young people, but one that could be improved upon, and: (1) YouthBuild increased the receipt of high school equivalency credentials; (2) YouthBuild increased enrollment in college, largely during the first two years. Very few young people had earned a degree after four years, and the program had a very small effect on degree receipt; (3) YouthBuild increased survey-reported employment rates, wages and earnings, but did not increase employment as measured with employer-provided administrative records, which might not include certain kinds of employment, such as jobs in the gig economy and other types of informal work; (4) YouthBuild increased civic engagement, largely via participation in YouthBuild services. It had no effects on other measures of positive youth development; (5) YouthBuild had few effects on involvement with the criminal justice system; and (6) As with many youth programs, YouthBuild's benefits through four years do not outweigh its costs. But it is too early to draw firm conclusions about YouthBuild as an investment, since the benefits accrue over participants' lifetimes. YouthBuild has continued to evolve since it started in the 1970s and even since the study began. The findings from the evaluation can inform its future direction and help it have greater impact. [For summaries of the three previous evaluative studies, see "Helping Young People Move Up: Findings from Three New Studies of Youth Employment Programs" ED590014.]