A Quiet Kind of Thunder by Sara Barnard

Steffi has been a selective mute for most of her life – she’s been silent for so long that she feels completely invisible. But Rhys, the new boy at school, sees her. He’s deaf, and her knowledge of basic sign language means that she’s assigned to look after him. To Rhys, it doesn’t matter that Steffi doesn’t talk, and as they find ways to communicate, Steffi finds that she does have a voice, and that she’s falling in love with the one person who makes her feel brave enough to use it.