The common finding of positively sloped age-earnings profiles is generally attributed to accumulation of human capital with work experience over the life cycle.3 Taken at face value, these results suggest that the relationship between literacy skills and age does not follow the pattern displayed by other forms of human capital. A 35-year-old in 2012 may differ from a 25-year-old in 2012 both because she is older and because she comes from an earlier birth cohort. Those born in different time periods may experience differences in the nature and quality of schooling and work experience, as well as differences in the contributions of other influences on skills such as parents and peers.