Communicating reasoning and constructing models fold nicely into a geometry activity involving the building of nesting boxes.
Sherri Ann Cianca
Wendy P. Ruchti and Cory A. Bennett
Solutions coupled with drawings can illustrate students' understandings or misunderstandings, particularly in the area of proportional reasoning.
Nicole R. Rigelman
Take a page from the humanities and have your students investigate mathematics in writing.
Jeffrey M. Choppin, Carolyn B. Clancy, and Scott J. Koch
Allowing students to reason and communicate about integer operations, or any idea, before these ideas are formalized can be an important tool for fostering deep understanding.