This paper offers an explanation for why workers in richer countries have faster rates of wage growth over their lifetimes than workers in poorer countries by providing theory and evidence on the differences in firm-provided training across countries. We document that the share of workers who receive firm-provided training increases with development, and that this is a key determinant of worker human capital investments.We then build a general equilibrium search model with firm-training investments and frictional labor markets. Our model suggests firm-training accounts for a large share of the cross-country wage growth differences. We find that self-employment is the key factor explaining the lack of training in the poorest economies, whereas labor market frictions are key to explaining training differences as countries develop. Finally, our model predicts considerable inefficiencies in human capital investments and sizeable aggregate gains from training subsidies to firms, which may be particularly desirable in poor countries where economic environments disincentivize training.