Accountability policies assume that educators will use student data to improve student learning, but data use in practice has turned out to be harder than theorized. The purpose of this article was to examine how science teachers in Grades 5 to 8 used data in their classrooms. Utilizing sensemaking theory, we found that teachers decided how to use data based on district and school policies and expectations around assessment and data use, balancing those messages with their own understandings of science education. In practice, this led to the privileging of certain kinds of assessment and data use at the expense of others.