This paper describes one way in which students can develop durable local identities in science classrooms. When students enter new classrooms or lab groups their identities are indeterminate, to varying degrees. Over time, however, students and teachers generally come to identify a given student in robust and predictable ways. The process of developing a stable local identity is intertextual. A more durable identity emerges across events, as signs of identity come to presuppose a consistent trajectory of identification that extends across events. The various trajectories of identification that an individual could have traveled normally get narrowed down, as events of identification become indexically linked along a more rigid trajectory. Such objectification of identity across a trajectory is only provisional, however, as aspects of identity can solidify and then change across events as well. This paper traces the social identification of one student across the course of a two month curriculum unit, showing how he developed a complex but robust identity across several weeks in a new lab group. The analysis first describes entextualization within classroom events, showing how the focal student was positioned in increasingly recognizable ways over a few minutes in one lab group activity. Then it traces the student’s emerging trajectory across many such events, showing how his identity solidifies, and in some respects becomes fluid again, as he gets identified across events. The paper also shows how this solidification depends on conceptual and physical resources particular to science classrooms, including resources drawn from the curriculum. Thus the paper shows one way in which the objectification of academic subject matter and the objectification of classroom identities can interrelate, when the solidification of social identity is facilitated by academic resources.