Many teachers have developed "tried and true" lessons that they look forward to teaching-- mystery powders is one that these authors like. Originally part of the Elementary Science Study curricula in the 1960s, there are now many different versions of this well-known activity in which students examine physical and chemical properties of several white powders (flour, cornstarch, baking soda, and so on) in order to identify a "mystery powder." With the release of the "Next Generation Science Standards" ("NGSS" Lead States 2013), some teachers may either fear they will have to let go of these cherished lessons, or may think that their lessons already align with the "NGSS." The authors noticed key differences between how they had implemented "mystery powders" and what is envisioned by the "NGSS." For example, while the activity aligned with performance expectation PS1-3, Make observations and measurements to identify materials based on their properties, they realized that they focused more on students correctly identifying the mystery powder than how they constructed arguments based on evidence. In doing so, they overlooked an important practice of science. In this article, the authors share how they adapted the mystery powders lesson for fourth and fifth graders using a 5E instructional model (Bybee et al. 2006) to emphasize the scientific practice of argumentation.