Research on family background and educational success focuses almost exclusively on two generations: parents and children. This study argues that the extended family contributes significantly to the total effect of family background on educational success. Analyses using the Wisconsin Longitudinal Study show that, net of family factors shared by siblings from the same immediate family, factors shared by first cousins account for a nontrivial part of the total variance in children's educational success. Results also show that grandparents', aunts', and uncles' socioeconomic characteristics have few direct effects on educational success. Furthermore, resources in the extended family compensate for lacking resources in low-SES families, which in turn promote children's educational success. The main conclusion is that the total effect of family background on educational success originates in the immediate family, the extended family, and in interactions between these two family environments. (Contains 9 notes, 4 tables and 3 figures.)