Abstract:This reaction paper is written from the perspective of a researcher whose work in the learning of algebra has primarily been with 12- to 16-year-olds. To provide some context for the comments and questions I will be raising with respect to the set of papers contained in this collection, I begin with remarks of a theoretical nature, first focusing on distinctions between arithmetic and algebraic thinking, and then elaborating the main components of algebraic activity. Against the backdrop of these theoretical remarks, I discuss some of the differences and similarities among the described curricula regarding the development of algebraic thinking. Lastly, I offer a definition for algebraic thinking in the early grades that is integrated within an existing model of algebraic activity in the later grades.