How do I get an S?! Kennen cannot be mastered?!

Ok so I recently started playing Kennen since I havent played him since season 3(like a lot of people) I've been having some really good games with him and right now I have a 5 win streak with him between ranked and draft. I have him at mastery lvl 5 and some of my scores are in the 700 or higher area and i have kda's like 15/1/13. I understand CS is a large part and I usually end up with almost 200 at the end of most games. Ussually by the ten minute mark I have 50-60. Can someone tell me why I cant get an S with kennen in top or mid?

Edit: I would like to thank DAEMANIC and Entropy Aether for responding in less than 2 minutes of this post going out. Hopefully their soultion will help me get an S. If anyone else has something to add for other players then go ahead, but depending on results I may or may not come to check. Thanks guys! ~Gardaen Patch 6.11 Bronze 3 Kennen Mid/Top Main

FINAL EDIT: I just played a game going 9/3/9 as Kennen in blind picks pvp. Used several more pink wards than usual and had a creep score of about 130-140 at the end of the game since I was playing mid and had quite a bit of action fighting Taliyah. At the end of the game without party bonus I had an A. I figured during a game with my friends since I would have 100 party bonus and a better kda and cs, I can now pull off an S- or S to S+. Thanks for the tips!