The evolution and evaluation of an elementary level structured immersion program in English as a second language are described. The program provides all academic instruction in English, but at a level that students can understand. It is ungraded, uses bilingual teachers who speak the students' native language, and has both developmental and direct instructional components. Vocabulary is carefully controlled and lessons are carefully sequenced to build on students' existing knowledge and proficiency. Evaluation of the program was undertaken through administration of the Comprehensive Test of Basic Skills, with the Language Assessment Scale as a supplemental measure of language skills. Two analyses were performed. In one, the performance gains of children in grades 3-6 were found to be significant in almost all academic areas tested. In the second, performance gains of non-English-speaking and limited-English-speaking children at the end of grade 2 and enrolled in the program for at least two years were compared with children not enrolled but within the same school district. Students in the program achieved and maintained above-median performance in all areas. It is concluded that structured immersion programs can be effective and warrant further consideration. (MSE)