This paper contributes a theoretical framework informed by historical, philosophical and ethnographic studies of science practice to argue that data should be considered to be actively produced, rather than passively collected. We further argue that traditional school science laboratory investigations misconstrue the nature of data and overly constrain student agency in their production. We use our "Data Production" framework to analyze activity of and interviews with high school students who created data using sensors and software in a ninth-grade integrated science class. To understand the opportunities for students to develop act with and perceive agency in data production, we analyze in detail the case of one student as she came to use unfamiliar technologies to produce data for her own personally relevant purposes. We find that her purposes for producing data emerged as she worked, and that resistances to her purposes were opportunities to act with and perceive her own agency, and to see data in new ways. We discuss implications for designing science learning experiences in which students act as agents in producing and using data.