Lelouch has middling grades because he's lazy, Suzaku has middling grades because he's stupid, Kallen has top grades because she's a hard worker.
But Lelouch is the most naturally gifted in intelligence of the three
I'm a bit disappointed in Diethard's loyalty, I'd expect him to be one of the more trustworthy of the Black Knights. He's given his all for Zero afterall.
Rakshata is surprisingly loyal, I guess Birtannia pissed her off at one point?