We aim to bring together two current strands of research into inequalities in individuals' educational attainment that are associated with their social origins: that concerned with the "primary" and "secondary" effects of social origins in creating inequalities, and that concerned with the relation between these inequalities and different components of social origins, taken to represent different forms of parental resources. Our main findings are the following. The secondary effects of social origins-their effects via the educational choices that young people make given their prior academic performance-are clearly operative across five key educational transitions within the English educational system. More specifically, we estimate that 35% of the total effect of social origins is secondary in the earliest transition that we consider, and from 15% to 20% in the subsequent four. Furthermore, mediation analyses reveal that secondary effects are most strongly associated with parental education and then, to a lesser degree with parental status, while little association exists with parental class and none at all with parental income. Primary effects are also at all transitions most strongly associated with parental education and status but in this case both parental class and parental income do retain some importance. We suggest an explanation for our empirical findings as resulting largely from the concern of highly educated, professional parents, and their children to avoid the occurrence of downward intergenerational mobility, especially in terms of education and status.