Just like his father, Calvin seems to enjoy all kinds of sport activities; be it watching or participating in one. He has tried Taekwondo in school and still plays football at the park. Recently, he has requested to be coached for badminton.
I will try to collect as many information as I can in the sports he is interested in.
He can gain some knowledge on string tension and how it can affect power, control and feel of the game reading Step-by-step on how to string a badminton racket. That way, he will know the kind of string he needs and precisely what sort of string tension suits him.