This question is impossible to answer. Depends, depends, depends.
How intense? I see players practice at wimpy intensities and others go animal.
How focused and well designed is the practice? A great practice design can accomplish in 1 hour what someone else might in 3 hours.
What is being worked on? Some developmental issues require a slow and long practice to work out and other allow for short but intense practices.
Where is the kid in terms of mindset? If they love tennis they might work for many hours with passion, others might be going through stages where tennis is not their #1 priority at the moment. They need less intensity more fun to get them over the hump and not lose them forever.
How about stages of growth? Are they dealing with growing pains and need less intensity? Are they in a teen stage where they need to rest more?
So many factors go into this topic, it is only possible to know the right number of hours on a case by case basis.
Last edited by TennisCoachFLA; 01-05-2012 at 04:50 AM.