My worst year popularity-wise was tenth grade. Every day I walked from the New York City subway station to school and back again - alone in the midst of crowds of friends. This trauma is in the book, true to life.
Through a special program in my junior high I skipped eighth grade. However, I repeated kindergarten, so it evened out. Still, it would have been handy for writing the book if I'd had eighth grade to look back on. To make up for my missing material, I spent a day with an eighth grade class and interviewed a bunch of eighth graders by phone. They told me about their subjects in school and what they did after school, and a little (I was shy; they were shy) about kissing, a crucial aspect of my research!