One of the fundamental tasks of the sociology of education is thus to discover what actions, by what people, in what social organisations, contribute to what extent in bringing about social differences in educational achievement.  
Lauder, Hugh (Editor); Nash, Roy (Editor). Explaining Inequalities in School Achievement : A Realist Analysis.
Farnham, Surrey, GBR: Ashgate Publishing Group, 2010. p 259.

The difficulties involved in developing and testing theories capable of providing robust explanations prove, however, to be unexpectedly severe. the sociology of education has, for example, never conceded that it possesses no adequate technique that will allow fractions of the disparity between social classes, such as that between the upper and lower fifths of the household income distribution, to processes localised to the home rather than the school.