Through a comparison of the widely-held traditional view of science with the constructivist view of science, we argue that the constructivist view of the content of science has important implications for classroom teaching and learning. This alternative view of science concepts as human constructs, scrutinised by application of the rules of the game of science, raises many challenges for teachers. Reconceptualisation of teachers' views of the nature of science and of learning in science is important for a constructivist pedagogy. We argue here that open discussion of the 'rules of the game' of science would contribute to better learning in the classroom, since learners would be better equipped to change their existing concepts by knowing more about the nature of science itself.