Our article "Understanding the mobility chances of children from working-class backgrounds in Britain: How important are cognitive ability and locus of control?" examines the role of cognitive ability and peoples' sense of control over their lives in mediating the effects of individuals' social background on their educational attainment and on their labor market position (Betthäuser et al., 2020a). The article takes as its starting point the persistent view in both academic and policy circles that most of the differences in the educational attainment and labor market success between individuals from different socio-economic backgrounds are due to differences in cognitive ability between them (see e.g., Marks, 2014;Murray, 2012). Using data from the 1970 British Birth Cohort Study, 1 we find that cognitive ability mediates a non-negligible yet limited amount of the effect of individuals' social background on their educational attainment (about 35%) and their labor market position (about 20%). This means that about 65% of the effect of individuals' social background on their educational attainment, and about 80% of the effect on their labor market position, is channeled by factors other than cognitive ability. Contradicting the claims by Murray (2012), Marks (2014), and others, this finding highlights that the intergenerational reproduction of social (dis)advantage that prevails in even the most developed societies is deeply unmeritocratic and unfair.Consequently, we see an urgent need for researchers to identify and for policy makers to address the channels through which individuals' parental class background shapes their life chances, above and beyond its effects on individuals' cognitive ability.In his commentary on our article, Gary Marks (2020, p. 3) concludes that the findings of our article "are technically correct but unimportant." He argues that examining the role of cognitive ability in mediating the association between individuals' social background and their educational and labor market outcomes is not a relevant exercise, since there are "only moderate associations of class origins with educational and occupational outcomes" (p.2). Instead, he suggests that research should focus on the importance of individuals' genetic predisposition and cognitive ability in affecting individuals' educational attainment and labor market outcomes (p. 2). In short, MarksThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.