The "Waldo" books, which require the reader-viewer to find the peripatetic backpacker amid thousands of tiny, scurrying figures, hold a fascination for young readers. And "Waldo" also builds reading skills. Here's how.
In order to find the Waldo character, the child must focus on the page, recall what he looks like from the first page, and compare and contrast that memory image with each figure on the page.
Thus attention span, recall and visual discrimination -- three essential skills of reading -- are nurtured. Finding Waldo is not terribly far removed from the recall and discrimination necessary to tell the difference between the letters "b" and "d" or between "p" and "q."
-- from "The Read-Aloud Handbook," by Jim Trelease