The Next Generation Science Standards (NGSS) have brought a stronger emphasis on engineering into K-12 STEM (science, technology, engineering and mathematics) instruction. Introducing the design process used in engineering into science classrooms simulated a dialogue among some educators about adding the arts to the mix. This led to proposals for a STEAM (STEM + arts) curriculum, as well as warnings that integrating the arts would weaken STEM instruction. The study summarized in this article tested the hypothesis that the arts might provide upper-elementary students, who were still concrete thinkers, with a powerful means of envisioning phenomena that they could not directly observe. This study investigated the impact of STEAM lessons on physical science learning in grades 3 to 5. Ten out of the 55 high-poverty (Title 1) elementary schools in a large urban district were randomly chosen as treatment schools and divided into two cohorts. Using a quasi-experimental design that holds general student scientific achievement constant, the study found that students exposed to the STEAM lessons demonstrated greater improvement on physical science benchmark assessments than students exposed to a STEM-only physical science curriculum.