We analyse in detail the factors that lead to intergenerational persistence among sons, where this is measured as the association between childhood family income and later adult earnings. We seek to account for the level of income persistence in the 1970 BCS cohort and also to explore the decline in mobility in the UK between the 1958 NCDS cohort and the 1970 cohort. The mediating factors considered are cognitive skills, noncognitive traits, educational attainment and labour market attachment. Changes in the relationships between these variables, parental income and earnings are able to explain over 80% of the rise in intergenerational persistence across the cohorts. Appended are: (1) Comparability of noncognitive measures; and (2) Variables. (Contains 1 box, 2 figures, 11 tables, and 10 notes.)