Backwards Day by S. Bear Bergman
This children's book, set on the planet Tenalp, introduces us to a world where there are seventeen seasons, including one where bubblegum falls from the sky for three days and a single day when everything - everything everywhere - is backwards. Andrea looks eagerly forward to Backwards Day every year, so she can turn into a boy for the day. But one year she doesn't turn along with everyone else. She's miserable. The very next day, however, she turns into a boy - and stays that way! He's delighted, but his parents are distressed, and take him to the big city to consult with Backwardsologists. When they finally figure out what's happened, the miracles of Backwards Day are fully revealed to the reader. This book is illustrated by New York cartoonist KD Diamond.