Reported is a study to compare three methods of oral presentation of science activities to fourth grade Spanish-speaking children. The methods of oral presentation used were: (1) an entire English presentation; (2) an entire Spanish presentation; and (3) a bilingual presentation. The investigation was conducted in two elementary schools in a low-socioeconomic area with a population of over 99 percent Spanish-speaking people. Six classes, three high-ability level and three low-ability groups, matched on IQ and results of a bilingual dominance test, were involved. The content of science sequence activities was the same and all the teaching was done by the investigator. The criterion variable was the children's achievement on predetermined concepts and skills as measured by a pretest-posttest. Based on the findings (.05 level of significance), the following conclusions seemed justified: (1) children taught by the simultaneous use of English and Spanish achieved more than those taught exclusively in English or in Spanish; (2) children taught exclusively in Spanish achieved more than those taught exclusively in English; and (3) there was no difference in achievement between children in the high- and low-ability tracks. It was recommended that Spanish-speaking children similar to those in this study be taught using the bilingual presentation method. (Author/EB)