Both endogenous growth theory and the (augmented) Solow model propose a role for human capital in the growth process though each is based on different conceptual arguments. Since both approaches can justify the inclusion of human capital levels and growth rates in an output growth regression the two theories cannot readily be distinguished empirically. This paper argues that the variable most commonly used in empirical studies to proxy human capital (levels or growth) - school enrolment rates (SERs) - may capture both stock and accumulation effects, but changes in SERs can provide useful additional dynamic information on the contribution of human capital to growth. Empirical evidence from samples of developed and less developed countries during 1960-85 suggests important growth effects associated both with 'initial' levels of, and changes in, SERs. The nature of these effects appears to differ between the two country groups.