See, for instance, Fournier and Koske (2012), Ponthieux and Meurs (2005). See Chapter 1 of the 2011 edition of Going for Growth (OECD, 2011e). Although it can take up to a generation until all the GDP per capita gains from such reforms are realised, small improvements labour force skills can produce large gains in future GDP per capita (OECD, 2010b). The direction of the change in relative returns depends on many factors, in particular the substitutability or complementarity between low- and highly-educated workers.