The report's first section, "What Questions Should the Evaluation Address?" emphasizes that evaluations should not only determine a program's impact but also the need for the program, its design, its implementation, and its cost-effectiveness. The second section, "When Is It Appropriate to Conduct an Impact Evaluation?" advises that this should be determined in the course of planning to launch the program and will depend on various factors that bear upon the evaluation. The third section of the report discusses how an impact evaluation should be designed. This involves practical and technical considerations related to sampling and the generalizability of results, statistical power, measurement, methods for estimating program effects, and information that helps explain effects. This is followed by an outline of how the evaluation should be implemented. The organizational infrastructure and procedures that support high-quality evaluation are then described. Recommendations accompany each section. 65 references