The Framework and NGSS emphasize using lines of evidence to construct explanations and develop arguments that demonstrate understanding about scientific phenomena. For this vision to be actualized in science classrooms, students must engage in investigations where they reason about their established lines of evidence as they construct explanations of phenomena. Reasoning about the evidence they have gathered enables students to construct and then defend explanations through argumentation. However, there is a blurriness for many teachers around these contemporary science practices. The purpose of this article is to clarify these practices by (a) identifying characteristics of explanations and arguments, (b) delineating how to engage students in science practices that develop lines of evidence they can use to make sense of phenomena, and (c) offering guidance on how to scaffold explanations and arguments around a local phenomenon. In this article I use the example of Niagara Falls, which is a local phenomenon for my middle school science students. Contemporary standards require a shift in classroom culture, instructional practices, and students’ understanding of what it means to learn science. This article helps middle school science teachers make this shift.