Grades, Ranking
noun
You become exploits... as in, your exploits become a thing you can actually see, and you can see them in the form of grades. Ouch, some of your exploits weren't all that amazing...
せいせき
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
家庭教師の先生のお陰で、成績がグンと上がりました。
My grades have gotten a lot better thanks to my personal tutor.