This is the first of a series of three articles, undertaken by the ERIC Center for Science and Mathematics Education, on three national elementary science projects (Elementary Science Study, AAAS--Science - A Process Approach, Science Curriculum Improvement Study) sponsored in part or in whole by the National Science Foundation. Six areas are generally covered for each of the three programs: (1) nature of the program; (2) instructional materials; (3) use of materials; (4) implementation and teacher programs; (5) evaluation; and (6) the role of the teacher. An important aspect of Elementary Science Study (ESS) materials is that they have been developed and designed according to how children respond as they work with the materials. ESS has placed great emphasis on having children work with concrete objects instead of ideas. About 60 units have been developed, with teaching guides, and are now in commercial production. Some of the units are designed to be used by an entire class at the same time. Other less structured and more open-ended units may involve only a small group and may not be taught as a series of connected lessons. Some units are definitely designed for individual or small group work. ESS has an active workshop program to acquaint personnel with ESS and assists schools in the implementation process. (BR)