This study estimates the lifetime effects of lost classroom instruction on labor market performance. For identification, I use historical shifts in the school year schedule in Germany, which substantially shortened the duration of the affected school years without adjusting the core curriculum. The loss of classroom instruction was mainly compensated for by assigning additional homework. Applying a difference-in-differences design to social security records, I find adverse effects of the policy on earnings and employment over almost the entire occupational career. Plausible mechanisms behind the deteriorated labor market outcomes include unfavorable effects on human capital and a differential occupational sorting.