I just had a game where I was 9/1/11 and I roamed a ton getting kills for my team and myself, I had fairly decent farm and not even an S- ? I've had so many great games but no S's? So what is the secret? Because it surely isn't reflective on how well you do..
Buy popstar
then after every kill release a hawt new mixtape.
Should get you s+ every time [slayer-pantheon-thumbs]
I JUST played a game as and got an S. I can't link it (it doesn't show up .-.) but I do remember what happened:
12/0/1, about 250 cs, placed 2 
s, placed a lot of 
s, killed drag once... however, our whole team didn't take a lot of towers.
I really think Riot needs to change their system. Comparing how you do to other people playing your champion isn't that great, but all I'd say is just keep trying. Ward as much as you can, that can really raise your grade.
towers, just last hit the towers.
The formula so far is being involved in tower takes, high kill participation, decent KDA, solid CSing, involvement in other objectives, and how your performance compares to others who play the champion. I think warding might be taken into account, I'm not positive.
CS better.
You need to ward and farm greatly since those are both more of a factor than kda
I played a game just today and I was 13/1/4 placed lots of and I had 87 cs. I had lots of games like that but I always had a bad rank I think it is about the time because it was all in 20min so in 20 min to have that score you have an S for sure but you also have to do lots of damage and kill some monsters.All I know is that you have to have a good score like 20/1/7 in minute 30 or 40 it is hard as Ahri main but eventualy you will get that S rank
Easy way: play her outside of mid. Hard way: git gud and pop off.
I had a game with 20/1/12 and 252 cs and I got an A+ too. it depends on the time the game lasts and the cs, the wards and how good other players play at the moment ahri. Its for example really hard to get a S on akali because Akali is a very strong champion who normally has a lot of kills.
But just keep going, once you will get a S :D
I got an S+ recently, with the game lasting 16 minutes, and a KDA of 707, which I believe to be important. I got a crowd control score of 10, and about 5.5 thousand damage to objectives. I dealt 47000 damage in total. I only placed three wards though, so I don't think its that important. I only came away with 55 creep score though... Only killed one tower. Hope this was useful.
I got 34/4/12 103 cs and i still didn't get an S I got an A WHAT THE HELL IS GOING ON RITO PLS FIX
I went 16/0/9 on and got only and S- so in order to get s your probably need to go 20/0/13 which is insane but who am i to judge. It should be noted that kill streaks get you a rank faster than getting kills one by one.
Bro What do you mean i got a 19/0/17 game with ahri and 122cs and put a LOT fo wards and still got an A
I went 17/1/19 with 220 cs for but I only got an s-, i was expecting an s or higher
It's reflective of how well you do compared to others on the same champ in the same role.
Ahris is popular and pretty powerful in the right hands, so the top tier performances are pretty darn good, so you'll need pretty intense a KDA on top of good farm. That said, KDA/CS isn't all there is to grades, warding, kill participation, objective participation, etc are all also factors to grades.
Well the jungler almost had as much CS as you. Maybe 200+ by the 40 minute mark would've gotten you an S-, I'm not sure but I've heard it's heavily decided by CS. Also, just curious, did the Janna get an S- at least? Cause the Janna did great.
