Mean school SES also appears to be related to student achievement. For instance, Lee and Smith (1995) found that school SES was strongly related to gains in science. In additon, Marsh (1991b), in an analysis of High School and Beyond data, also found a relationship between the composition of schools and adolescents' achievement, finding that the higher the average level of school SES, the higher students test scores were. This relationship was found even after controlling for important background characteristics.