To determine the relative importance of school and individual factors in the determination of science learning, achievement test scores were analyzed in relation to individual- and school-level factors in a national sample of about 2,000 tenth-grade students participating in the Longitudinal Study of American Youth. Hierarchical linear analyses showed that individual measures accounted for most of the variance. Previous achievement was the preponderant influence on subsequent achievement. Nonetheless, initial science attitude, instructional time, the home environment, and exposure to mass media were also significant individual-level influences on science achievement. (Author)