Sarah Prineas's The Magic Thief echos Sara Monette's Labyrinth books in having a thief befriend a magician. Luckily there aren't many other similarities, because Monette's books are not exactly elementary school fare, and Prineas's books came recommended by my fifth grade son. I have not responded by handing him Melusine, though. I recommend Monette to the rest of you, though.
In The Magic Thief, Conn meets a wizard by picking his pocket without dying. Intrigued, the mage brings him home, even though the mage's burly minion thinks he's bad news (wow, this reminds me of Monette again!). Conn is determined to be a wizard; he feels an affinity for magic that baffles the older magicians around him.
The story moves along, showing off the other wizard's apprentices, the political maneuvers between the Duchess, the wizards, and the sinister Underlord, who has some kind of connection with Conn. His past continues to haunt him; it's hard to trust a boy who has been a thief all his life, and it's hard for that boy to trust others. I guess Conn is a little too good to be true, but I like that in a story. I give this book an A-, and recommend it to kids around fourth grade (3rd through seventh?). I'll be grabbing the sequel in a week or so.