This study analyzes the effects of a missing high school graduation cohort on firms' training provision and trainees' wages. An exogenous school reform varying at the state and year level caused the missing cohort to occur. Using administrative social security data on all trainees and training firms, we show that firms provide less training by reducing their overall number of hired apprentices. We also show that the pool of firms that offer training in the year of the missing cohort shifts towards a higher share of low wage firms. After keeping firm characteristics constant, the findings indicate that the missing cohort increases training wages measured at the start of training. Further analyses shed light on the opposite case of dual cohorts, which we find to increase training provision and to decrease training wages. The evidence also shows that high and low wage firms differ in how they adjust training provision in response to a dual cohort.