This volume provides an examination of the theoretical basis for preschool through elementary school multiage grouping, a realistic picture of what it looks like, some guidelines for planning and implementing a multiage model, and recommendations from practicing multiage teachers. Chapter 1 defines multiage grouping and provides a brief history of the movement. Chapter 2 supplies the theoretical framework by examining which theories contribute to the creation of a solid foundation upon which multiage grouping is built. The theories are cognitive, social learning, sociocultural, psychosocial, and ecological. Chapter 3 provides the readers with the common beliefs and the curricular, instructional, and assessment elements inherent in multiage settings. Chapter 4 describes four sites that are currently using multiage models. Chapter 5 follows with some down-to-earth advice on how to get stared and how to be assured that a program will be solid enough to overcome some of the barriers that are inherent in any change. Chapter 6, the final chapter, pulls all the pieces together by providing teachers' perceptions of advantages and disadvantages, as well as advice and encouragement. A glossary and an index are included. (Contains 63 references.) (JB)