The problem is further exacerbated when making this assessment by the fact that juniors cannot always be judged by their chronological age; the physiological factor is a far more reliable indicator, which is made even more complicated when to the causal observer the slighter the child the harder they seem to run more so than the more rounded and seemingly stronger junior. So rule one is that you should not be overtly concerned about those who are not qualified to judge what a junior should or should not be doing. The most important aspect for the coach is to be fully aware of what the youngster is actually capable of doing without too much stress, and that a record of the training progression is available for reference.
If juniors are grouped together for training then this individualised approach - in most cases - does not exist and there can be times when certain juniors in a group session can be stressed unduly. It is extremely important that sufficient groups exist to cater for a range of abilities and that qualified coaches are there to supervise. If a regular attendance at training sessions is undertaken by a junior it soon becomes apparent what that junior is capable of, and if the continuity of the same coach allows for regular assessment then progression through the groups can be made without undue concern.
More rapid progress can be made if a junior is individually coached with sessions specifically tailored to that athlete. The levels of intensity can be observed much more closely and individual records kept to record progress. Juniors should not be allowed to unduly influence the sessions with their enthusiasm. If progression is to be carefully monitored then the total weekly workload has to be considered, including school sports and that all training is part of a schedule that is pre-planned.
So how much is enough? There are guidelines on how much training certain junior age groups can undertake, but they are so general in content that they are of little use other than for those just starting their running career, and are not for those juniors who have been running for several years. There are other words of wisdom from a variety of sources that unfortunately indicate a conflict of opinion, all from internationally respected coaches. Some say that specialization should not be undertaken before the age of 18, and that intensive training is severely restricted up to that age, and in some cases should not start until athletes have matured both physically and mentally.
Tim Noakes says that the period of time that an endurance athlete can maintain form in international competition is about 10 years - and considering that the age band of 25 - 35 is considered the best period for that form, starting too early would jeopardize that purple patch. Grete Waitz’s advice is that children should not specialize in middle distances (800m to the mile) before 13 - 14 years of age or in long distances (up to 10k) before 15 - 16 years of age. Paula Radcliffe is currently the epitome of what all juniors want to accede to, and as someone who started running at the age of 11, she is still going pretty strong with 19 years under her belt!