A generalized evaluation model (GEM) has been developed to evaluate primary prevention program impact. The GEM model views primary prevention dynamically; delineating four structural components (program, organization, target population, system) and four developmental stages (initiation, establishment, integration, continuation). The interaction of the four structural components as the prevention effort moves through the developmental stages provides the focus of the evaluation. GEM emphasizes processes to specify factors that contribute to a program successfully reducing or preventing instances of physical, cognitive, emotional, or social impairment. (Author)