This paper analyzes the differences in the relative roles that family social background and family process variables play in the development of achievement and motivation at the individual and at the aggregate or school level. The particular data analysis model employed treated the attributes of the school a student attended as if they were his own attributes. Although this allowed correlations to be generated which formed the bases for regression and commonality analyses, it resulted in difficulties in interpreting the amounts of variability found for each source of variation. Although data was collected on grade levels one, three, six, nine, and twelve, the most reliabile results were for ninth graders. There is a pronounced tendency for students of similar social background to go to school together. This tendency is also pronounced for "Achievement," but not for "Motivation." In explaining the behavior of students and schools the same relative roles are played by the social background and family process sets of variables for expectations, attitude toward life, and study habits but not for educational plans and achievement. Differences in these relative roles at the individual and aggregate level may occur because already large relationships between social background and other variables are further accentuated when students are allocated schools on the basis of social background. (Authors/JM)