At a ceremony at Hay Festival, the 10 shortlisted young authors introduced their books and each gave a short reading.
The winner said that three years ago she had planned out the structure and characters of her book, then went to The Bookseller YA event at Hay Festival, which inspired her to get it written. Goodbye, Perfect is the story of Bonnie a teenager about to sit GCSEs, who runs away with the Head of Music. Sworn to secrecy, her best friend Eden is forced to weigh up betraying her friend in her secret location with telling the truth to the police and suspicious parents, and dealing with her own doubts about this 'perfect' girl.
Barnard said that the nub of the story was not the girl running away with her teacher, "but how that affects those closest to her and the people left behind". This is her fourth book. She wins £2,000 – and much greater exposure.
The other shortlisted authors were: Juno Dawson, Laura Dockrill, Muhammed Khan, Louise o'neill,, Alice Oseman, Tom Pollock, Fiona Shaw, Katherine Webber and Laura Wood.
The YA Book Prize is awarded annually to a young adult novel written by an author in the UK or Ireland. It aims to get more teens reading and buying books.
Laura Bates, writer and founder of Everyday Sexism, and one of the judges, said, "Sara Barnard's writing is an absolute triumph; this book is unputdownable and beautiful, unflinching in its exploration of important and complex topics, from sexual exploitation to the foster care system. But it is also a joy to read, a tender portrayal of family and sibling relationships, of flawed and poignant female friendships and of the nuanced reality of teenage experiences and the journey to discovering who you are and what you stand for."
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