How do Workers Learn? Theory and Evidence on the Roots of Lifecycle Human Capital Accumulation

How do the sources of worker learning change over the lifecycle, and how does this affect human capital and wages?

How do the sources of worker learning change over the lifecycle, and how does this affect human capital and wages? Using data from Germany and the US, we document that internal learning (from coworkers) decreases with experience, while external learning (on-the-job training) follows an inverted U-shape. We develop a search model featuring multiple learning sources whose returns evolve as workers age and accumulate human capital. Quantitative results indicate that the interaction between sources is key to lifecycle wage dynamics and the effects of remote work, which disrupts internal learning and early-career wage growth, though external learning partially offsets these losses.