The Resolving Conflict Creatively Program (RCCP) is a comprehensive, school-based program in conflict resolution and intercultural understanding implemented in more than 110 New York City public schools. The National Center for Children in Poverty is currently conducting an evaluation of the program in grades 1-6, although the program itself is implemented in grades K-12. The following components are included: teacher training, classroom instruction and staff development, the program curriculum, administrators' training, peer mediation, parent training, and a targeted intervention for high-risk youth. The program evolved out of practice-based theory. Researchers and practitioners have collaborated on and designed an evaluation that illustrates how the practice-based theory is consistent with and can be put into operation using developmental and ecological theories of the etiology of violence-related behaviors in middle childhood. The target population for this study is approximately 9,600 children, 5-12 years of age, in 15 elementary schools in New York City. The evaluation is being conducted over two years with two data-collection points in each year. A cross-sequential design is being used to examine the short- and intermediate-term utility with children at different ages/developmental stages. The relative effect of the beginning program can be compared to more comprehensive models. A total of 8,233 students responded to the baseline survey. The study population is largely Hispanic (41%) and African American (37%). Preliminary analyses indicate that baseline means of such constructs as aggressive fantasies, hostile attributional biases, and conduct problems increase with grade level. Ten years of practice-based experience and one year of a two-year quantitative evaluation have taught several important lessons about school-based program implementation and the evaluation of such programs. The scope and longevity of the RCCP and the empirically rigorous evaluation now under way will make a significant contribution to the field of violence prevention and field-based program evaluation.