It is hard to measure talent. IMHO, it's how they see and feel the board. Talented child can visualise the board without seeing it.
For example, ask him to close his eyes and tell all the squares on e1-a5 diagonal (or something similar). Check how easy or difficult it is.
Of course, it's not exhaustive
__________________
For private coaching email
IgorGoldenberg@bluebottle.com
Computer tells you what to play, a good coach explains why.
The urge to save humanity is almost always a false front for the urge to rule.
H. L. Mencken