The Pawn by Lucy Auburn

Four boys rule the halls of Coleridge: Cole, Lukas, Tanner, and Blake. They call themselves the Elites, and together they decide who deserves to be part of the upper echelon.
Two months ago they harassed my twin brother until he took his own life.
Now I’m going to take his place at the academy, and take my revenge on them one by one. I’ve been studying these boys for months. I know just exactly who and what they are—and how to destroy them.
But what if I’m wrong?
What if, in the middle of the storm, there’s a sharp, painful truth?
One I fear to face, because it might mean that my brother lived as he died: broken inside, and willing to hurt others.
Justice is a messy thing in the hands of a girl with nothing left to lose…