It is well-known that there are large disparities in academic achievement between children of different socio-economic status (SES) backgrounds. This study examines the evolution of disparities in literacy skills between adults of different SES backgrounds. It compares countries’ patterns in the evolution of disparities in literacy by SES background as cohorts age and asks which patterns of educational and labour force participation predict a narrowing rather than a widening of these disparities. Since there is no international longitudinal study of skills across the entire adult life span, this study uses three cross-sectional international adult studies (International Adult Literacy Survey, Adult Literacy and Lifeskills and Programme for the International Assessment of Adult Competencies) and matches birth years to create synthetic cohorts. Results indicate that there is large cross-national variation in the evolution of skills disparities associated with SES background. Disparities in literacy proficiency tend to widen when SES disparities in high school completion, professional and blue-collar employment increase. Disparities narrow when workers exit the labour force, a finding that is explained by the large inequalities in the employment experiences of individuals from different SES backgrounds, measured by differences in use of literacy skills at work. These results help to explain cross-national variation in the evolution of skills disparities by SES background, which has implications for policies aimed at closing skills gaps over the life course.