This article analyses the contribution of post-compulsory education and training systems to the development of literacy and numeracy skills across OECD countries. While there is extensive cross-country comparative research on the effects of primary and lower secondary education systems on aggregate skills levels, there has been little comparative analysis of system effects after the end of lower secondary education. This article uses a quasiâ€cohort analysis of the tested literacy and numeracy skills of 15-year-olds in [Programme for International Student Assessment PISA 2000 and 27-year-olds in the 2011 OECD Survey of Adult Skills (SAS) to estimate the gains in different countries in mean levels of competence in literacy and numeracy. We found that Nordic countries (Norway and Sweden) with comprehensive upper secondary education and training systems and German-speaking countries (Austria and Germany) with dual systems of apprenticeship were particular[ly effective, whilst countries with mixed systems (England, Ireland, Northern Ireland and Spain) showed a relative decline in both literacy and numeracy. The education system characteristics that account for these differences are (a) the inclusiveness – as proxied by high rates of participation at 17/18 and low social gradients of level 3 completion; (b) the esteem of vocational programmes; and (c) curriculum standardisation with regard to the study of maths and the national language.