Justin Morgan Had a Horse by Marguerite Henry

[Aladdin] Joel Goss knows that Little Bub is a special colt, even though he's a runt. And when schoolteacher Justin Morgan asks Joel to break the colt in, Joel is thrilled! Soon word about Little Bub has spread throughout the entire Northeast -- this spirited colt can pull heavier loads than a pair of oxen. And run faster than thoroughbreds! This is the story of the little runt who became the father of the world-famous breed of American horses -- the Morgan.