I love this picture on stages of development. Pinterest.com has a host of ideas of incorporating play into the curriculum!
Another reliable source has always been Dr. Seuss. I love these quotes on education. They are encouraging, inspirational, and right on time! Dr. Seuss always provides a meaningful message, though the presentation is fun to students. He uses his imagination to create worlds of characters who work through situations. Schools should provide the same opportunities for students to imagine, create, and explore character development.

