The unsuspecting mage : book one of the Morcyth saga / Brian S. Pratt.

Enhanced descriptions from Syndetics:

Magic Real Magic Ever wanted to learn? We require someone with intelligence and a disciplined mind. Those well versed in fantasy novels and role-playing games a plus. May need to travel. Only those of good character need apply. No appointment necessary. When he answers an intriguing advertisement in the newspaper, James couldn't possibly have known that it would thrust him into the middle of a quest that will test the limits of his intelligence and courage. James, a high school senior, is not given any sort of explanation why or how he's been brought to this strange, mystical world. He quickly realizes that he's able to use the knowledge he's gained through reading hundreds of books as well as the time spent in role-playing games to help him cope. The world he's entered is one on the edge of war, and only by learning to control the magic within himself will he be able to survive the trials ahead. With the help of a boy named Miko, James sets out on an adventure across this strange world to discover why he's there-and what he must do. For more about The Morcyth Saga, go to: morcythsaga.com