In this study, meta-analysis techniques were used to synthesize research on the effectiveness of three major activity-based elementary science programs (ESS, SAPA, and SCIS), which were developed with federal support. In 57 controlled studies, outcomes were measured in over 900 classrooms; the overall mean effect size for all outcome areas was .35. The mean effect size was .52 for science process tests, .16 for science content, and .28 for affective outcomes. On the average, gains also were realized in creativity, intelligence, language, and mathematics. Only 3 of 14 coded study features were related to reported effects: Disadvantaged students derived greater benefits than other students; tests not biased in favor of the activity-based programs resulted in positive but lower effects than those favoring the activity-based approach; and published reports had higher effects than unpublished reports. The effects of particular programs reflect their relative curricular emphases. In three followup studies, student groups that had had activity-based programs in elementary school and had later experienced traditional science programs during middle school years could not be consistently distinguished from control groups.Various aspects of the science curriculum reform period have been examined by reviewers over the years. Lockard (1963)(1964)(1965)(1966)(1967)(1968)(1969)(1970)(1971)(1972)(1973)(1974)(1975)(1976)(1977) cataloged the appearance and disappearance of curriculum projects. Welch (1979) chronologized its history. Weiss (1978), through surveys, andStake &Easley (1978), through case studies, documented the use of programs and the reactions of school personnel and on-site observers. Many researchers, especially doctoral students, investigated effects of implementation and teacher training efforts and effects of the new programs on students and teachers. Smith (1969) and Gallagher (1972) presented early narrative reviews of this work. In addition, periodically, the Educational Resources Information Center (ERIC) at Ohio State and the journal, Science Education, have published summaries of studies of the programs. Most recently meta-analyses of studies evaluating the effects of the reform programs on teaching practices and