This paper demonstrates that heterogeneity in firms’ promotion of human capital accumulation is an important determinant of life-cycle earnings inequality. I use administrative micro data from Germany to show that different establishments offer systematically different earnings growth rates for their workers. This observation suggests that that the increase in inequality over the life cycle reflects not only inherent worker variation, but also differences in the firms that workers happen to match with over their lifetimes. To quantify this channel, I develop a life-cycle search model with heterogeneous workers and firms. In the model, a worker’s earnings can grow through both human capital accumulation and labor market competition channels. Human capital growth depends on both the worker’s ability and the firm’s learning environment. I find that heterogeneity in firm learning environments account for 40% of the increase in cross-sectional earnings variance over the life cycle, and that this mechanism is especially important for young workers. I then show that differences in labor market histories partially shape the worker-specific income profiles estimated by reduced-form statistical earnings processes. Finally, because young workers do not fully internalize the benefits of matching to high-growth firms, changes to the structure of unemployment insurance policies can incentivize these workers to search for better matches.