This four-year project will develop a program for kindergarten through sixth grades that fosters the development of number sense concepts through a problem- solving approach.l The program will provide conceptual edperiences to promote students' understanding of number, quantity, and operations. It will model new teaching strategies and content for elementary mathematic instruction. The projecat will develo;p, pilot, and evaluate three units per grade level. Each unit will be two tothree weeks long and have a dual focus: to deepen students' understanding of mathematical concepts and to develop their interpersonal skills and commitment to values of caring, fairness, and responsibility. The units will provide opportunities for students to explore number concepts as they cooperatively investigate problems and communicate about their thinking and learning. The units will be devel;oped through a process that includes repeated trials in classrooms by teachers and CMP staff. The units will be published by Addison-Wesley. An evaluation will assess: (1) how teachers use the materials in their classrooms; (2) how participation in a staff development program influences teacher implementation; and (3) the impact of the program on student concept attainment and teachers' and students' attitudes about mathematics.