ABSTRACT
Traditionally the most important factor in the design of science teaching materials has been the structure of the knowledge to be taught. The student's prior conceptions are seen to influence the sense they make and the meanings they construct in science classes, whether from practical activities, text, or discourse. As a consequence of the research into student's prior conceptions, it has been recognized that promoting conceptual understandings of school science involves students in a process of conceptual change from prior conceptions towards school science ideas. Analyses of the conceptual change process both in students and in the history of science indicate that it is a slow and difficult process with many constraints acting to oppose change. Current developments in promoting conceptual understanding in science have drawn attention to the importance of considering learner's prior conceptions in the design of teaching programmes.
