I think that page numbers will be difficult to give because every edition contains different pagination.  In the end, you are going to have to match up specific events listed with where they happen in your version of the text.  The first and most pressing event in the book is the rape of Melinda at the hands of "it."  Adding to this would be her calling the cops to break up the summer party as to where it happened.  The social ostracizing of Melinda at the hands of the high school social order in the First Marking period are three events that are interlinked as cause and effect realities of one another.  These three help to set the stage for the rest of the narrative.  The growth and emergence of cliques and Melinda's response to them as she is alone might be another element to discuss that is of importance.  I think that noting the reaction that Melinda has to her teachers would also be of importance in the identification of important events.  The discovery of "her place" as the janitor's closet might also be important because it marks the specific realm where her transformation is able to take place.  Along these lines would be the growing admiration that Melinda has of David, who listens to his own voice and "speaks" in a manner that Melinda wishes.  In confronting the memory of Melinda's horrific night over the summer in the "Third Marking Period" section, the seeds are sown for her reclamation of voice.  In the last section, the emergence of Melinda as an artist, the appreciation others have for her work, the desire to be "reborn" as a tree, and the confrontation of "it" and her declaring that "I said 'No," are all critical events.  In the end, noting that Melinda begins the process of opening up to Mr. Freeman, after she was supported by members of the Lacrosse team helps to close the novel, but open the narrative of Melinda's reclamation of voice.