At no time in history has improving science education been more important than it is today. Yet after 15 years of focused standards-based reform, improvements in U.S. science education are modest at best, and comparisons show that U.S. students fare poorly in comparison with students in other countries. In addition, gaps in achievement persist between majority group students and both economically disadvantaged and non-Asian minority students. In part, these achievement gaps mirror inequities in science education and take on greater significance with the looming mandate of the No Child Left Behind Act. This report answers three broad questions: 1) How is science learned, and are there critical stages in children’s development of scientific concepts? (2) How should science be taught in K-8 classrooms? (3) What research is needed to increase understanding about how students learn science?