Many students find it easier to express their ideas about science through talking rather than writing. However, writing in science promotes new learning, helps students consolidate and review their scientific ideas, and aids in reformulating and extending their scientific knowledge. These practices lead to formulating and defending scientific explanations. To support elementary students in the complex practice of science explanations, teachers first must provide experiences for students to observe phenomena before asking them to explain the phenomena. To illustrate the role writing can have on creating explanations, this article describes how the authors implemented a framework referred to as CER (Claim, Evidence, and Reasoning) to achieve the "Next Generation Science Standards" ("NGSS") practice of Constructing Explanations. The CER framework supports the development of explanations and guides young children in communicating their understandings of science through writing. This framework supports students' learning and writing through forming statements (claims) based on their observations (evidence) and then discussing these results with respect to the underlying scientific principles (reasoning) to build a deeper understanding of the content. The activity presented in the article is designed for upper elementary students. The purpose of the activity is three-fold: (1) for students to gain an understanding of how the properties of matter affect light and sound; (2) how these effects are related to each other; and (3) to practice formulating explanations.