This longitudinal study investigated the influence of social class and family socialization on the development of cognitive competence, educational performance, and academic attainment; the interdependencies between the development of cognitive competence and educational performance; and the impact of social class, family socialization, cognitive competence, and educational performance on academic attainment. Participating were urban Icelandic children and adolescents, from ages 7 through 21 years. Social class was defined by the nature of parents' work, education, and income satisfaction. Restrictive and supportive socialization conditions were classified as factors derived from social network affiliation, time with child, control strategies, and child rearing styles. Cognitive competence was measured at 7, 9, 12, and 15 years by aggregated scores on a battery of Piagetian tasks. Academic performance was measured by grade point average, and educational attainment was represented by the educational level achieved by age 21. Results indicated that social class had a larger impact on educational performance and academic attainment than on individual cognitive competence. Family socialization influenced all outcomes. There was a minor direct influence of cognitive competence on academic attainment, mediated by educational performance. Thus, educational attainment was importantly influenced by social class, while cognitive competence was not. While the results confirm findings about the respective influence of social class and family socialization on the development of competence and educational performance, they differentiate between the effects of background variables and process variables on educational outcomes at different levels. (KB)