We aim to bring together two strands of existing research into inequalities in individuals’ educational attainment associated with their social origins: that into the relative importance of the primary and secondary effects of social origins; and that into the relative importance of different components of social origins, indicative of different kinds 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 we consider, and from 15-20% in the subsequent four. Further, 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. Finally, secondary effects on educational transitions appear to be top-driven. There is a clear tendency for their importance to be greater in the case of young people with highly educated, professional parents as compared with those of all other social backgrounds. We suggest an explanation for our empirical findings as resulting largely from the concern of such parents and their children to avoid the occurrence of downward intergenerational mobility, especially in terms of education and status.