Abstract: In collaborative work with teachers over the past five years, we have found that students in kindergarten through fifth grade are thinking about ideas that are at the heart of algebra. In the course of working on arithmetic, students notice regularities that might, in later years, be expressed with symbols and equations. These ideas offer opportunities for rich mathematical investigation and discussion that provide access to foundational ideas about the operations. We are currently investigating how students who are struggling in mathematics and students who typically need more challenge in mathematics engage in this work. In this talk, I will give an overview of our work and engage participants in considering some classroom cases.