Why does the schoolhouse in holes go from worn down to a jewel of a building?

The schoolhouse turns into a jewel of a building because Onion Sam helps fix it up. Over time..... he makes it beautiful.

By the end of the first semester, Onion Sam had turned the old run-down schoolhouse into a well-crafted, freshly painted jewel of a building that the whole town was proud of. People passing by would stop and admire it. "That's our schoolhouse. It shows how much we value education here in Green Lake."