One major responsibility of teachers preparing an optimal learning environment for young children is to provide many types of materials so that children, during the large blocks of exploration time provided each day, may choose for themselves how to elaborate their own skills in each area of development. In addition, teachers must select materials that can be used for helping children become familiar with routines and materials associated with activities presented in an instructional format. The principles for selecting materials for children of any age (including infants) and for any type of activity involve the following criteria: appropriateness (or developmental match), versatility, variety, safety, function, durability, and aesthetic qualities. (MP)