J. Scott Savage's books for years, especially his Far World Series.
In Far World, Kyja, a young girl, has grown up without the ability to do magic, thinking of herself "cripple" despite the encouragement of her friends, including Master Therapass, a wise, elderly wizard, and Riph Raph, a skyte. (Skytes are like tiny flying dragons, about the size of a chihuahua.)
Meanwhile on Earth, Marcus, the same age as Kyja has grown up needing a wheelchair to get around, but at the same time having the strange ability to turn himself slightly invisible, which has always puzzled him. Once they meet, via Kyja seeing him through an "Aptura Discerna" and pulling him to Far World in time to save his life, things start falling into place. They come to realize they need the help of the Elementals of (Water, Land, Air, and Fire) in order to save both their worlds, and the adventure begins!
I've enjoyed this series, and recommend it to readers young and old, who love fast moving, clean fantasy!