The academic achievement of 144 second, third, and fourth graders in two Tucson elementary school bilingual education programs was measured by pre- and post-test scores on the California Achievement Test (CAT) and California Test of Basic Skills-Spanish (CTBS) in the fall and spring of the 1982-83 school year. The study was undertaken to examine whether or not the students gained in achievement during the school year, how students changing from Spanish to English reading and math instruction compared with those initially placed in English instruction, and how gains compared on the two tests. Significant differences were found between fall and spring scores on the CAT reading and math tests in each grade, and in the CTBS in second and third grades. Fourth-grade students receiving instruction in Spanish reading and math showed no gains on the CTBS. However, students changing from Spanish to English instruction in the third grade performed significantly better on the CAT math test. No significant differences were found for fourth grade students changing from Spanish to English. Further research with greater controls was recommended. (MSE)