"Freak the Mighty" by W.R. Philbrick

Maxwell Kane is too big and tall for his age. He's constantly teased and harassed at school due to his size and learning disability. He lives with his Gram and Grim, after his father (Killer Kane) was sent to prison for murdering his mother.

Kevin, nicknamed Freak, has a unique size, too. Due to a genetic birth defect, Freak is much smaller, and relies on crutches and braces to get around.

Max and Kevin are neighbors and they form a very unique friendship. Kevin uses his brain and Max uses his size and together they form "Freak the Mighty," and they fend off the bullies together.

This is a fantastic story of overcoming adversity, and the power of great friendships.