Social programs are often based on unclearly articulated theoretical rationales. The evaluations of these programs are also often relatively theory free, and therefore make limited contributions to theory. A Program Development Evaluation (PDE) approach, intended to integrate theory testing with the development and evaluation of action programs, is described and illustrated. This approach has been applied for over 2 years in the national evaluation of locally developed delinquency programs in 69 schools, and has resulted in (a) the implementation of several true experiments conducted in collaboration with project implementers, (b) an increase in the clarity of projects' theoretical rationales, and (c) the identification and measurement of theoretical intermediary variables as well as outcome variables. Based on the action research paradigm, the PDE approach appears to increase the theoretical and practical relevance of evaluation research. (Author/PN)