This report summarizes the National Job Training Partnership Act (JTPA) Study, which examined the impact of Title IIA of JTPA on participants' employment, earnings, and welfare receipt. Between 1987 and 1989, more than 20,000 adults and out-of-school youths who applied for JTPA services in 16 areas across the country were randomly assigned to a "treatment group" or to a "control" group that was ineligible for JTPA-funded services for 18 months but that remained eligible for all non-JTPA-funded services in their communities. This study evaluation report covers the following topics: origins and goals of the national JTPA study; the study's setting and design; the JTPA program in the study sites; implementation of random assignment within the JTPA program; service receipt by treatment and control groups; sample size, data collection, and related issues; and site selection and the study's external validity. Profiles of the study sites are appended, 37 exhibits are included. (Contains 23 references. (MN)