The Weasleys were the only Gryffindors to stay at Hogwarts for Christmas, since their parents were visiting Bill in Egypt. So they had the run of the tower, which the twins at least took full advantage of. Ron, however, was by now very attached to the idea that studying made him a better person. And if there wasn't much you could say about his enthusiasm for knowledge, still it would be hard to suggest that he was the kind of person who lacked for stubbornness. So he picked up his books and his stack of imperfect homework assignments and sat with Percy, studying close enough to the fire that they could roast things and eat them as they worked.