It is very standard for Coaches and Training Facilities to both expect and ‘sell’ parents on the fact that the young athletes in their care will become decidedly better in only 6 or 8 weeks’ worth of training.
And in fact, they’re correct in saying so.
But not because their training system is somehow superior or because they possess unique talents as a Coach, quite simply, it’s because human beings are adaptive machines that alter (become better) under the strain of applied demand (training).
This is especially true for young people in the age bracket of 6 – 18. This time of life represents a literal coming of age with respect to maturation and athletic ability. The Central Nervous System is learning to master the art of movement, bones are growing more dense and muscles are becoming naturally longer and more powerful.
You could, quite literally, ask a 15 year old soccer player to run stairs 3 times per week for 6 weeks and show improvements to both their speed and power output capacity. That doesn’t mean running stairs is an efficient training style, it just means that the human body is designed to accommodate the stress it is placed under by getting faster and stronger.