For many, the dominant model of curriculum development in science includes generating a topic, clarifying science content, identifying activities associated with the topic, and figuring out an assessment. Unfortunately, this approach tends to overemphasize activities and underemphasize mastery of science concepts and the process of scientific inquiry. The National Standards for Science Education should stand as the learning outcomes for any science curriculum. However, educators also need to focus on how students learn; on integrating laboratory experiences with other activities in the classroom; and on ensuring rigorous, focused, and coherent content in the context of a curriculum that focuses on the process of scientific inquiry and the acquisition of conceptual knowledge. The Biological Sciences Curriculum Study (BSCS), with funding from the National Science Foundation, offers an effective alternative to the traditional high school sequence of biology, chemistry, and physics. Each year begins with a two-week Science as Inquiry unit, followed by three core units that last eight weeks each in physical science, life science, and earth-space science. The last unit of the year is multidisciplinary and examines compelling issues in science and society. Students who used the program showed average gains in science understanding of 20-25 percent.