My Father's Dragon by Ruth Stiles Gannett
Trade paperback format. Illustrated by Ruth Chrisman Gannett. Highly recommended! Read the rest of the trilogy, too -- Elmer and the Dragon, and The Dragons of Blueland.
When Elmer Elevator hears about the plight of an overworked and underappreciated baby flying dragon, he stows away on a ship and travels to Wild Island to rescue the dragon.
This book has been selected as a Common Core State Standards Text Exemplar (Grades 2-3, Stories) in Appendix B