Procedures and results of an evaluation of the Choctaw Bilingual/English as a Second Language (ESL) Program, conducted in east central Mississippi, are discussed. The program, which is in its fifth year, is implemented using Title VII funds in three of the six Bureau of Indian Affairs elementary schools on the Mississippi Choctaw Reservation. The Bilingual/ESL program focuses on increasing students' proficiency in English in a manner that does not devalue Choctaw language or culture. It involves formal classroom instruction and parent training. A major component involves the training of instructional personnel in ESL instructional methods. The means used to evaluate the project was the gap-reduction design advocated by G. K. Tallmadge et al. During the evaluation, the program served 139 students enrolled in kindergarten through grade 3. All students were dominant Choctaw speakers with limited English proficiency. A comparison group of 194 non-ESL students in kindergarten through grade 4 was used. Students in both groups were administered the California Achievement Test (CAT) in April of 1987 and 1988. The unit of analysis was the standard score for the reading, language, and total battery. Results indicate that the students in the program made greater gains in all three batteries of the CAT than did non-ESL students. It is concluded that the program has been sufficiently effective to recommend its adoption by the entire school system. In addition, the gap-reduction method of program evaluation has proven to be an efficient and effective method of evaluating supplemental educational programs. Nine data tables and five graphs are presented. (TJH)