In this article, the authors present a sequence of activities from a curriculum about light for third and fourth graders that supports students in learning to disagree like scientists. This sequence of activities helps students discuss reasons for the discrepancies in their data, use the language of argumentation in classroom discourse, and get a more accurate picture of science as a way of understanding the world, rather than just a collection of right answers (Driver, Newton, and Osborne 2000). (Contains 2 figures and 1 online resource.)