From the Executive Summary: "Rather than being based on hunches and best guesses, intervention programs are increasingly expected to be evidence-based. However, when evidence-based programs are replicated or scaled up, it is critical not only to know whether a program works, but which program elements are essential in making the program successful. To date, though, few programs have had hard data about which program features are critical "core components" and which features can be adapted without jeopardizing outcomes. What information is needed to select and implement programs that address the needs of the identified population? "Core components" include the functions or principles and related activities necessary to achieve outcomes. Strategies for a well-operationalized program include a clear description of the context of the program; the core components; the active ingredients to operationally define the core components so they can be taught and learned and can be implemented in typical settings; and a practical strategy for assessing the behaviors and practices that reflect the program's values and principles, as well as the program's active ingredients and activities. Also when outcomes are not achieved, an understanding of core components and whether they were implemented correctly is essential to understanding whether a program is ineffective, or alternatively, whether it was not implemented well . . . Since issues related to the core components of interventions are relevant to producing new knowledge about what works and for moving science to practice in socially significant ways, this brief is relevant for a range of professionals and stakeholders, including program developers, researchers, implementers, and policy makers."