Training studies have shown that cognitive plasticity, that is the potential modifiability of a person's cognitive abilities, is considerable across the lifespan and extends to very old age. Cognitive training can not only result in significant performance improvements on the trained tasks, but also benefit performance on new untrained tasks (transfer). However, even though interventions can be very successful at the group level, individual differences in training gains tend to be large. Why do some individuals benefit more than others? In the present study (N = 168), we investigated transfer of executive control training in children (N = 56, 8-10 years of age), younger adults (N = 56, 18-28 years of age), and older adults (N = 56, 62-77 years of age) in a pretest-trainingposttest design. Results of latent change modeling showed a training-induced reduction of age differences and individual differences across training and transfer tasks in all age groups. Moreover, individuals with lower cognitive abilities at pretest showed larger training and transfer benefits after the training. This effect was significantly higher in the training group compared to an active control group, indicating that it was based on the executive control training and not on non-focal effects (e.g., regression to the mean). These findings reveal a pattern of compensation effects with the largest training-induced improvements in participants who needed them the most.