Authors have argued that various forms of interventions may be more effective in younger children. Is cognitive training also more effective, the earlier the training is applied? We review evidence suggesting that functional neural networks, including those subserving attentional control, may be more unspecialised and undifferentiated earlier in development. We also discuss evidence suggesting that certain skills such as attentional control may be important as "hub" cognitive domains, gating the subsequent acquisition of skills in other areas. Both of these factors suggest that attentional training administered to younger individuals ought to be relatively more effective in improving cognitive functioning across domains. We evaluate studies that have administered forms of cognitive training targeting various subcomponents of attention and the closely related domain of working memory, and we contrast their reported transfer to distal cognitive domains as a function of the age of the participants. Although negative findings continue to be common in this literature we find that cognitive training applied to younger individuals tends to lead to significantly more widespread transfer of training effects. We conclude that future work in this area should concentrate on understanding early intensive training, and discuss a number of practical steps that might help to achieve this aim. (Contains 1 table and 3 figures.)