Representational Tools and Conceptual Change: The Young Scientist’s Tool Kit Kevin F. Miller University of Illinois at Urbana-Champaign We interpret the world and its regularities through representations and procedures that are a complex me ´ lange of formal experience, rules of thumb, and naive concepts that precede formal education. These representational tools give us the language in which we can think about science. Three propositions are argued: (a) that such tools are fundamental to scientific reasoning and science education; (b) that cognitive science has a great deal to say about how cognitive tools affect thinking and conceptual change, particularly how the representations intrinsic to ordinary language relate to the symbol systems of formal science and mathematics; and finally, (c) that cognitive science may play a role in developing representational tools that make scientific information more accessible. The metaphor of a scientist’s tool kit is a useful one in considering the development of scientific thinking and the roles of cognitive science in promoting science educa- tion. We interpret the world and its regularities through representations and proce- dures that are a complex me ´ lange of formal experience, rules of thumb, and naive concepts that precede formal education. These representational tools give us the language in which we can think about science. Cognitive science has a great deal to say about how such representations are acquired and used. Most of the examples herein concern symbolic tools for representing number, particularly Arabic numerals. Number is, to quote a book title, the language of science (Dantzig, 1954), the means by which scientific concepts are formalized and communicated. Furthermore, mathematics, with its regularities, is a particularly clear domain for considering how the organization of symbolic methods affects the ease with which people learn and use the regularities underlying those symbols. Direct all correspondence to: Kevin F. Miller, Beckman Institute, University of Illinois at Urbana- Champaign, 405 North Mathews Avenue, Urbana, IL 61801-2300 kmiller@s.psych.uiuc.edu. Journal of Applied Developmental Psychology 21(1): 21–25 Copyright  2000 Elsevier Science Inc. ISSN: 0193-3973 All rights of reproduction in any form reserved. 21