We formulate a two-country, two-good, two-factor endogenous growth model with learning by doing and intersectoral knowledge spillovers. Our model exhibits no transitional dynamics because of constant returns to capital, the existence of only one state variable for each country, and the factor price equalization theorem. By applying our model to the problem of aid and growth, we show that a permanent increase in untied aid raises the common growth rate if and only if the propensity to consume the capital-intensive good in the recipient country is larger than in the donor country.