My Gym Teacher Is an Alien Overlord by David Solomons
Zack and Lara have superpowers. Luke has new school shoes and a burning sense of resentment. He KNOWS that aliens disguised as gym teachers are about to attack Earth but will anyone listen? No. So one dodgy pact with a self-styled supervillain later, and Luke is ready to save the world. He just needs to find his trainers. 'My Gym Teacher Is an Alien Overlord' is the action-packed sequel to the bestselling 'My Brother Is a Superhero', winner of the Waterstones Children's Book Prize and the British Book Industry Awards Children's Book of the Year.