This study investigated the effectiveness of two English second language (ESL) teaching methodologies commonly used in bilingual classrooms: concurrent translation, often criticized but widely practiced, and dual language preview-review, which combines introductory and follow-up exercises in the first language and lesson teaching in the second language. Subjects were 60 native Spanish-speaking third-grade students of mixed Spanish and English reading skills, divided into three groups. One (n=16) was a control group, one (n=21) was taught using concurrent translation, and one (n=23) was taught using the preview-review method. All had the same teacher. Pre- and posttests of vocabulary acquisition were administered and analyzed. Results indicate that the children learned and retained far more vocabulary with the preview-review method. However, students taught with the concurrent translation method who took a delayed posttest performed better than those with a posttest immediately after treatment; this difference was not statistically significant. The findings support the use of preview-review in the bilingual classroom. Further research on the possible negative effects of the concurrent translation method, on long-term treatment effects, and on methods building on student background knowledge is recommended. A 57-item bibliography and the vocabulary test used are appended. (MSE)