The National Association for the Education of Young Children (NAEYC) website offers great resources related to understanding the importance of children's play - play based learning, why play is a key part of children's learning and development, and the role of play in the classroom.  The site provides insight into links between play and early learning academic standards.  Playdough, for example, is not merely a "fun" activity, but provides valuable hands-on, active learning experiences, supports children's growth and learning in many domains - and, through this medium, teachers can observe children's progress in many areas of development.