This bulletin is one of a series on the place of subjects in the elementary school curriculum. The first of the series showed how subject matter is introduced into the program in a modern school. The other bulletins in the series discuss how various skills, such as reading, creating in art, and writing are developed in the modern school program. This particular bulletin deals with how children learn to think. From several illustrations of children at work in the classroom, some principles about thinking and problem solving are identified. Children are most inclined to think when they are given an opportunity to think about how important it is to have a classroom environment in which good thinking is expected and encouraged. The examples given show how important it is to have a classroom environment in which good thinking is expected and encouraged. It is intended that persons who read this bulletin discover anew that opportunities to help children think abound in all phases of the school program. It is hoped that readers will find numerous suggestions here for using the opportunities that exist to develop good thinking habits in children. A bibliography is included. (Contains 2 footnotes.) [Best copy available has been provided.]