SOLVED. Teen dystopia novel published in the last 10 years. it's about a group of four girls (as displayed on the cover) trying to break free of an evil and corrupt society. [s]

[Hannah]

The group sneak in one girl who's poor and can't afford to go to the school their attending that is in the mountains. One girl gets punished by the head of the school and they overhear that the school plans on holding those not apart of their plot hostage. They break out with a group of boys from the same school across the lake and try to make their way home. There is one scene where they do outdoors survival training, but other than that they run amuck.
I distinctly remember the cover of the paperback. It was the four girls with their backs facing the perspective, in an empty but green landscape.

[Andria]

Maybe the Tomorrow Girls series? The first one is Behind the Gates

[Hannah]

You are a beautiful human being! I honestly didn't think this was going to work! Thank you so much!