Double stimulation is a principle of Vygotsky, according to which a subject, when in a problematic situation, turns to external means for support to be able to act. Contemporary literature on double stimulation examines concept formation and cognitive development without addressing the question of how the emergence of concepts is intertwined with the emergence of agency. This was, however, a central concern for Vygotsky and the continuing relevance of Vygotsky’s legacy largely resides in the relation between agency and double stimulation. Vygotsky used the experiment of the “meaningless situation” as a paradigmatic example of the principle. In this experiment, a subject is escorted to a room, asked to wait for the beginning of the experiment but the experimenter does not return. This design allows tracing how the participants start forming a concept of the situation. We carried out a series of experiments after the model described by Vygotsky. Experiments conducted with 22 groups are analyzed here to investigate how double stimulation is simultaneously a mechanism of conceptualization and agency. The data consists of videotaped and transcribed experimental sessions plus participants’ stimulated-recall interviews, also recorded and transcribed. The analysis focuses on both verbal and physical aspects of interaction.