How did Sakumo discover that Kakashi was a genius? What was the reason he was tested and sent to the academy so early?
This question is actually what inspired me to write my dad fic series XD
I’d say that the most likely theory would be that Sakumo was pressured to put Kakashi through for testing & academy admittance at an early age because he’s the Son of the White Fang and “has” to be talented, too; but I like to imagine that he did it because he thought that Kakashi needed the extra stimulation, since his intelligent little self was curious of the world around him & how everything worked, and he would have torn the house apart, otherwise 
Poor Sakumo nearly had a heart attack the day Kakashi found a lighter, learnt how to light it, and then, not knowing that fire burns things, nearly set himself, and the house on fire! 
How do you think Sakumo discovered Kakashi’s genius?