Exercise training represents a potent stimulus to the development of aerobic and anaerobic fitness in adults; whether the same is true in young children is unclear. With the possible exception of peak VO2, many parameters of aerobic and anaerobic fitness remain scarcely investigated in children, especially pubertal children. Despite this lack of empirical evidence, it has been suggested that children may lack trainability and that this may be related to the presence of a maturational threshold below which significant adaptations to training cannot occur. This suggestion requires investigation, not least because the findings of some studies which appear to support this contention may in reality be a reflection of the use of an inappropriate test modality or training programme for the investigation of training status influences. The purpose of this review is therefore to provide insight into the current consensuses and controversies regarding the influence of training in young people.