The Boy Who Lost Fairyland (Fairyland, 4) by Catherynne M. Valente

When a young troll named Hawthorn is stolen from Fairyland by the Red Wind, he becomes a changeling – a human boy – in the strange city of Chicago, a place no less bizarre and magical than Fairyland. Left with a human family, Hawthorn struggles with his troll nature and his changeling fate, while attending school and learning about human kindnesses – and un-kindnesses.