A study investigated the relationship between the 1982 native language proficiency of 4,700 newly-enrolled Spanish-speaking, limited-English-proficient (LEP) kindergarten through seventh grade students and their success rates in acquiring English proficiency in the following 4 years. Findings of the study, and the implications derived from the study, were examined for instructional program design. Results revealed that, for Spanish speakers, English acquisition is strongly related to native-language proficiency, and that, for the smaller proportion of students who become English proficient in one year, English proficiency at the time of enrollment is the best predictor of their subsequent second-language development. Based on these results, it is suggested that (1) educators make provisions for differences in first-language proficiency when they design bilingual programs for Spanish-speaking students; and (2) studies be undertaken to determine whether this relationship holds true for native speakers of other languages. (MSE)