In their contribution to this volume, Wertsch and Kazak turn to a theoretical tradition they trace to Vygotsky, as well as to the lesser-known Gustavovich Shpet. They argue that, viewed from the perspective of Vygotsky and Shpet, the goal of science instruction is to help students become fluent users of a sign system. From this point of view, instruction requires a sort of bootstrapping, in which students move from having little ability to use a sign system, to becoming fluent users of that sign system. In this commentary, I contrast the view of science learning outlined by Wertsch and Kazak with what I refer to as the conceptual change perspective. Based on this contrast, I argue that Wertsch and Kazak systematically underestimate what students know, as well as how much intersubjective overlap there is between student and instructor.