One tool for enhancing students' work with data in the science classroom is the measure line. As a coteacher and curriculum developer for The Inquiry Project, the author has seen how measure lines--a number line in which the numbers refer to units of measure--help students not only represent data but also analyze it in ways that generate understanding of key science projects. The Inquiry Project, led by TERC, an education research organization in Cambridge, Massachusetts, and Tufts University, engages children in grades 3-5 in science inquiry about the nature of matter. This article illustrates how measure lines are used in the project. (Contains 3 figures and 1 online resource.)