This paper examines inequalities in attainment in vocabulary and mathematics at age 16 for a nationally representative cohort of people born in Britain in 1970 (the 1970 British Cohort Study). Our analytical sample is n = 3,583 cohort members who completed vocabulary and mathematics tests at age 16. We explore whether inequalities as a result of childhood social background are similar across the linguistic and mathematical domains, or whether they differ, and to what extent these inequalities are accounted for by families' social class position, parents' education and home reading resources, as well as by children's own reading for pleasure. As reading can be seen as an indicator of "cultural capital", we also test the influence of an alternative indicator of cultural capital, playing a musical instrument. Our longitudinal analysis addresses the question of the extent to which differences in attainment are determined by age 10; and which factors are linked to a growth in differentials during adolescence. We show that childhood reading is linked to substantial cognitive progress between the ages of 10 and 16, whereas playing an instrument is not. Reading is most strongly linked to progress in vocabulary, with a weaker, but still substantial link to progress in mathematics. Strikingly, reading for pleasure is more strongly linked than parental education to cognitive progress in adolescence.