The English language achievement of 213 Spanish speaking students in grades K-3, who receive English as a Second Language (ESL) instruction in the context of a bilingual program, is compared to that of 104 similar students who receive ESL instruction within the traditional school program, in order to probe whether enrollment in a bilingual program retards the learning of English as a second language. ESL achievement, as measured by listening and reading comprehension tests, is compared through ANOVA and partial correlation analysis with a quasi-experimental evaluation design. Anlaysis of data indicates that students learning English in a bilingual program learn just as much English as students learning it through ESL classes within a traditional curriculum. Because the amount of measured English achievement in kindergarten and first grade is found disappointing compared to the substantial achievement measured in second and third grades, two questions are raised - that of the effectiveness of language instruction in K-1 and that of the appropriateness of the techniques used to measure achievement on these levels. Although the study needs replication with other age groups and other languages, the implication derived from the study is that half-day bilingual programs do not inhibit Engllish language achievement in primary-aged children. (Author/AM)