Abstract We develop a two-sector model of physical and human capital accumulation, in which the government may allocate resources to both sectors, thereby enhancing productivity. We analyze the impact of both the level of government spending and its composition on growth and welfare, and derive their respective growth-maximizing levels. We show that both the growth-maximizing and welfare-maximizing rates of allocation of public expenditure are independent of the way infrastructures are defined (flow or stock). This conclusion, however, does not extend to the dynamics of the model where the adjustment to fiscal policy is very different. After a tax cut, for instance, the growth rate of physical and human capital converge to the new equilibrium from opposite directions under the stock specification; whereas they converge from the same direction under the flow specification.