What characterizes a teaching practice that involves connecting arithmetic to algebra?  This workshop is based on the book, But Why Does it Work which describes a teaching model for engaging students in helping them identify, articulate, represent, and prove general claims that underlie computational strategies. This model also offers the opportunity to develop rich images of the operations and how they are different from one another, which is an important prerequisite to manipulating algebraic symbols meaningfully. During the two days participants will engage in mathematical argument to expand their own mathematical thinking, as well as, analyze student thinking and teacher moves through classroom video of lesson sequences.  Teachers will leave with access to lesson sequences that are designed for classroom implementation two to three times a week for fifteen or twenty minutes each over a two to three month period. Time will be given at the end to plan for a lesson sequence to be implemented in the classroom. There will be opportunities for extended learning support during the two to three month period while doing the lesson sequence in the classroom.