For systemic reform to occur, the allocation of students' and teachers' time will need to change significantly. Curricular reform will undoubtedly result in redistribution of the content of science education. The underlying theme of much of the content reform has been "less is more." As emphasis shifts from specific factual detail to underlying concept formation, science educators will need to rethink the way science is packaged for instruction. The subjects into which science knowledge is traditionally divided will be replaced by an integrated approach to science learning that emphasizes the holistic nature of scientific inquiry. Meanwhile, as laboratory experience replaces textbook study as the primary vehicle of instruction, both teachers and students will need more flexibility in how they spend their time. Above all, teachers need to be granted both the time and the opportunity for professional development if they are to break away from traditional practice, embrace a new way of teaching and learning, and use assessment methods that are embedded in instruction.