Principles of program evaluation research are outlined so that bilingual education program coordinators can conduct methodologically acceptable program evaluations. The three basic principles of evaluation research are: identification of the program participants, definition of the program intervention, and assessment of program effectiveness. Assessment of program effectiveness requires accurate measurements of how the students performed after program participation and how they would have performed without the program. Among the problems faced in evaluation design is the impossibility of a true experimental design in which limited English speaking students are randomly assigned to bilingual or nonbilingual education programs. In addition, subjects may be from a variety of cultural backgrounds and may enter the program at different ages. Finally, the concept of language proficiency is ambiguous, and a consistent concept and instrument must be used to assess language proficiency among all participants. (RW)