A number of studies have found that parental education is associated with adolescents' achievement. Conger, Conger, and Elder (1997), for example, found maternal education to be positively associated with GPA in grade 10, with adolescents whose mothers had higher levels of education reporting higher GPA's than those whose mothers had lower levels of education. Guo (1998), in an analysis of NLSY, found that adolescents whose mothers had more years of education had higher achievement test scores, after controlling for maternal cognitive scores and other background factors. Jordan and Nettles (1999), in an analysis of NELS data, found that family SES, a variable comprised of parental occupation status and family income, predicted math and science achievement in the 12th grade, with adolescents whose families had a higher SES performing better on tests of their science and math skills than those whose families had a lower SES. These relationship held even after controls were added for a number of background characteristics, such as 10th grade achievement, 10th grade self-concept, gender, race, hours worked, activities, and school-level factors. Gamoran (1992), in an analysis of High School and Beyond data, also found that higher levels of family SES, a composite variable comprised of parental education, family income, father's occupation, and home resources, predicted higher individual level math and reading test performance, after accounting for background and school-level factors such as school mean SES, school type, prior achievement, gender, race/ethnicity, and academic track.