The classroom that is the focus of the analysis reported in this paper was the site for a year-long first-grade teaching experiment. The goal of the classroom teaching experiment was to investigate ways to proactively support students' ability to develop strategies for adding and subtracting quantities. In addition, the project also focused on the teacher's proactive role in supporting students' mathematical growth in an inquiry mathematics classroom. Within the project classroom, the teacher often redescribed and notated students' responses so that what students had done mathematically might become an explicit topic of conversation. As part of this process, she frequently introduced either informal or conventional notation to record students' explanations of their mathematical activity. The introduction of these notational schemes led to students' development of ways of notating their own reasoning. In this way, the notation emerged from the students' activity while supporting shifts in their mathematical development.