A theoretical framework based on cognitive/developmental research is described. It is argued that science learning is a gradual process during which initial conceptual structures based on children’s interpretations of everyday experience are continuously enriched and restructured. Conceptual change also involves increased metaconceptual awareness, cognitive flexibility, and theoretical coherence. Some of the implications of this research for the development of science curricula and for instruction are discussed. It is also argued that while cognitive/developmental research can provide us with important information about the process of learning science, it does not provide much information about the external, environmental variables that can facilitate cognitive performance and conceptual change. What is needed in the future is the development of a theory of learning that bridges science education and cognitive/developmental research. Such a theory should specify the mechanisms that can take an individual from one level of cognitive performance to the next and relate them to situational and cultural factors.