His books have saved me on numerous occasions. I first encountered Elephant & Piggie when I worked at an after school program. Every single kid, kindergarten through fifth grade, LOVED "Today I Will Fly." The kids would read it every day and assign parts to each other. (Creative, right? Entirely their own idea!)
Maintaining order in kindergarten classrooms when substitute teaching became significantly easier if I brought a copy of Elephant & Piggie's "We are in a Book." (I never left the house without it.)
Most recently, I have found how fantastic these books are for early readers. Especially reluctant early readers.
~~The books are at a reading level (Guided Reading Level E-F from what I've found) that doesn't offer many other exciting options. I've found when my reluctant readers make a jump to Level D, they are excited because they are starting to feel like "readers!" But then, I bring them very typical beginning readers (like, "The cat and dog are friends. They like to play. They can share.") and they are super disappointed because they want a "real" book like their friends who have been reading for awhile.
Willems' books are "real" books that kids are excited about. So when they make that jump to a Level D or E, they get to celebrate the step with some characters they really like. Woohoo!
~~The Elephant & Piggie books are long. Do you remember when you read your first book that was 100 pages? Then 300 pages? These are milestones! When kindergarteners or first graders read an Elephant & Piggie book that is 60 pages long, they feel like they've accomplished something. Who cares if there is only one word on some pages? I've never met a kid who did.
~~ They think the books are hilarious, and they can't wait to find out what happens. Despite the length, these books don't require bookmarks. They will definitely be read in one sitting.
And now... I have found yet another use for Willems' books.
CCSS RL.K.7, RL.1.7 & RL.2.7-- Use the illustrations to describe characters.
[Side note: I love this standard. Do you? It emphasizes "reading" the pictures to understand the story. I like this connection to art as a means of interpretation. Even if the words are complex, most kids can describe what is happening in the pictures. Yay art!]
The book I've recently found for this standard is "Don't Let the Pigeon Drive the Bus." The Pigeon is such a strong personality, and his emotions and feelings come across so well in the illustrations. The little black lines Willems uses to depict the Pigeon's anger are fantastic and so succinctly get the point across.
Here's a worksheet for kindergarten (maybe first grade) that ties to the standard and the story. Enjoy!