Government agencies and members of the educational research community have petitioned for research-based curricula. The ambiguity of the phrase "research-based", however, undermines attempts to create a shared research foundation for the development of, and informed choices about, classroom curricula. This article presents a framework…

Fourth-grade students who participated in a yearlong, whole-class teaching experiment not only reconceptualized natural numbers but also generated flexible solution strategies to perform numerical computations mentally and in writing. Students' reconceptualization of number was mediated by their perceived resemblance between the physical action of…