All-new X-men Vol.3: Out Of Their Depth - Brian Michael Bendis

The time-displaced young X-Men continue to adjust to a present day that's simultaneously more awe-inspiring and more disturbing than any future the young heroes had ever imagined for themselves. And as Jean Grey pushes her powers to the limit, shaking her and the rest of the X-Men to the core, one of the All-New X-Men breaks rank and leaves to join the adult Cyclops and his revolutionary crew! They never warned us about this sort of thing in temporal mechanics class! Collecting All-New X-Men #11-15.