Nick is well into an extensive critical discussion of François Laruelle's philosophy in his postings on accursedshare. Thanks, Nick!
A study along these lines provides a first indication of how some of these social characteristics may be related to performance in college. If a factor is not causally related to the outcome, then the population possessing this factor should have the same performances as the population lacking this factor (the null hypothesis). So if we find that differences in family structure or performance in high school are associated with differences in college performance, then we can infer that these factors play some causal or structural role in the outcome.
However, these findings do not establish specific causal linkages among the factors. Take the hypothetical finding about family income: is this statistical discovery the result of this mechanism (greater family income provides more support for tutoring and academic support) or this mechanism (greater family income is associated with familial values that put strong emphasis on successful completion of university degree) or this mechanism (greater family income confers social advantages that make completion easier for affluent students)? In other words, the statistical discovery does not determine the nature of the causal relation between the antecedent condition and the outcome; it simply points the researcher towards investigating the concrete social mechanisms that might be at work here.
The example demonstrates an important lesson about social inquiry. Statistical study of a population can in fact point us towards some preliminary hypotheses about social causation. But these statistical discoveries are only the first step. In order to confidently assert causal relationships between things like income and race, to educational outcomes, we need to arrive at a nuanced analysis of the social relations and institutions through which these gross factors play into individual outcomes. We need to have an account of the mechanisms and processes through which the effects of concrete social settings characterized by differences in family structure, SES, race, or schools play out in the social psychology and educational opportunities that determine the ultimate outcomes of the young people who pass through them.
(A similar line of thought can be found in this posting on the problem of sorting out the data establishing correlations between race and asthma.)