I've notice that no matter what I do, it's impossible for me to get an S-. I've had incredible games where I've totally carried my teams yet all I ever get is A+. This is what it looks like every time I get an A+, incredibly close to S- every time http://imgur.com/a/MGwyV. This has happened about 15 times now and no matter what I can't get an S-, so I was wondering if anyone knows why this is happening.
Grades I think honestly take in account of every factor, amount of objective damage (inhibs, towers, dragons)
and then theres also the KDA factor, getting good KDA is more of an early game thing, if you finish the game below 30 minutes going like 8-0-10 you'll probably gettin an S or S- but then theres also farm
you need a good 70+ farm per 10 minutes for a good grade (jungle works differently)
damage to champs probably also takes an affect and I think one of the last things that also takes an affect on your grade is the champ you play, if you do really good with a higher win rate champ you're more likely not to get an S
and as for Jungle a lot of statements have been made that getting an S in the jungle is harder than any other lane, yesterday i went 12-0-8 as 
and had a good 200 farm in like a 32 minute game, but because shes busted and i was jungling and probably didnt do much damage to champs as other people on my team i got an A+.
It's difficult to pinpoint an exact reason your score was held back, but grades take into account a variety of factors other than your KDA such as CS, warding, objectives, damage/healing etc. Something in your gameplay is too low. Just try to improve your gameplay in all aspects and don't focus on one thing (many think a high KDA alone is how you get a great score, it isn't).
CS is probably the most important factor in determining grade. For jungle, you want to make sure to have at least 5 CS per minute (jungle monsters).
In the same boat. I went 7/0 in a 4v5 AND we won the 4v5. B+
wtf. Im sorry but cs shouldn't be everything. I only got 94cs, but i still deserve at least and A.
