As Chapter Eleven shows, Jess' response to Leslie's death seems to follow a fairly typical pattern of going through a huge gamut of different emotions. Firstly, he meets the news with complete denial, refusing to believe that it can be true and feeling that if he runs away it will not be true and Leslie will still be alive, as the following quote demonstrates:
He ran until he was stumbling but he kept on, afraid, to stop. Knowing somehow that running was the only thing that could keep Leslie from being dead. It was up to him. He had to keep going.
The two short sentences at the end of this paragraph demonstrate how he has shut down rational thought, so shocked is he by the news of Leslie's death, and all else is out of his mind, only the fact that he has to keep running. The short sentences therefore illustrate his single-minded fixation on what he is doing. Then he descends into numb disbelief, before going through guilt and anger before he is finally able to begin to process what happened. One of the reasons why this book is so successful, and rightfully so, is through its realistic depiction of a child's grief.