On February 13, 1940 Call It Courage was published by The MacMillan Company, the story about a young boy on the island of Hikueru in Polynesia written and illustrated by Sperry.
Although established as a writer, Sperry continued to illustrate dustjackets for other well-known authors of young adult fiction of his era, including Howard Pease, Agnes D. Hewes, Edgar Rice Burroughs, Florence C. Means, and Hildegarde Hawthorne, as well as illustrating various basal readers for the Ginn Co.