Building number sense with Number Worlds:a mathematics program for young childrenSharon GriffinDepartment of Education, Clark University, 950 Main Street, Worcester, MA 01610, USAAbstractNumber sense is easy to recognize but difficult to define and hence, to teach. In this article, number senseis defined in terms of the knowledge known to underlie it, as identified in cognitive developmental theory andresearch. A preK-2 mathematics program, called Number Worlds, that was specifically developed to teach thisknowledge is described and five instructional principles that lie at the heart of the program, and that are groundedin recent theories of learning and cognitive development, are used to illustrate several of its features. Evidence ofthe program’s effectiveness in teaching number sense and in enhancing the mathematics learning and achievementof at-risk children is briefly presented.© 2004 Elsevier Inc. All rights reserved.