Doodle did a lot with his short life of five years. He surprised everyone by living longer than three months and walking, but he went even further than that and surprised his brother with unconditional love and hero worship, which his brother, at times, felt he didn't deserve at all. For example when his brother, the narrator, pushed Doodle into the water and Doodle almost drowned, but his brother saved him, all Doodle cared about was his brother saving his life, not the fact that it was his brother who put it in danger in the first place. Doodle also surprises everyone by going beyond just simply walking to rowing a boat and running. He pushed his little deformed body to its absolute limits to please his brother. Doodle also surprised his brother with his carefree attitude toward life because Doodle didn't care that he was different, he knew it didn't matter and he only tried to be "normal" for his brother.
Doodle accomplishes two very important things that no one believed he would ever be able to do. First, he lived past three months. The doctors had convinced the parents that there was no hope for their child, so they even had a small coffin made for him. To everyone's surprise he did live beyond three months, and when the story ends he is five years old. His second great accomplishment was that he learned to walk. Because his head was too big and he had a strange backward crawl, it was assumed that he was incapable of walking. He got around by being pulled in a wooden cart by his older brother. When his brother turned thirteen and became self-conscience of having a little brother who was different, the two determined that Doodle would walk. And he does.