Here is a book (grades 3-6) based on a true story that I guarantee will be loved by many students:
The One and Only Ivan by Katherine Applegate.
Ivan is an easy-going gorilla living at a run-down mall that also doubles as a zoo. He is happy enough with his friends and his life until one of his animal friends dies from neglect and a new baby elephant, named Ruby, arrives. Ivan soon realizes he must help Ruby escape and the book becomes a story of friendship and hope, told with humor and love.