My author is Chris Crutcher.  In the past they wrote Period.8, Whale talk and many more.     I think he wrote this book for many reasons.  One reason is to show that people should stick up for themselves without being scared of anybody else.  Another reason is to not be mean to people unless you know their story.  Sarah is not scared to stand up for her and Eric.   Also people are making fun of Sarah's scars and Eric's size when they don't know her story.