Freak The Mighty by Rodman Philbrick
Maxwell Kane is feared and bullied because of his slowness and enormous size. With his father in jail for murdering his mother, nobody expects much of him. Kevin, the new boy next door, on the other hand, is smart, quirky and funny with an insatiable curiosity and a zest for life. But Kevin suffers from a rare genetic condition, whcih means he has a bent spine and can't walk without crutches. Yet the combination of Kevin and Maxwell is formidable, and together they become Freak the Mighty.