The National Council of Teachers of Mathematics (NCTM 1991, 2000) recommends that students be positioned as sense makers who weigh one another's ideas and judge their mathematical validity. The instructional tool discussed in this article helps students engage in discussions that foster student reasoning, then settle on correct mathematics.…

Understanding logical necessity is an important component of proof and reasoning for teachers of grades K-8. The ability to determine exactly where young students' arguments are faulty offers teachers the chance to give youngsters feedback as they progress toward writing mathematically valid deductive proofs. As defined, logical necessity is the…