Having an answer to "When are we ever going to use this in real life?" is important to middle school mathematics teachers. The activity described in this article awakened sixth graders' understanding of how artists use mathematics. By exploring ratio and proportionality in different paintings, students realized the use of proportional reasoning in artistic compositions. In this article, they share a lesson created for middle-grades students using a new game app called Keys to the Collection, developed by the Barnes Foundation in partnership with Drexel University's School of Education. This lesson was implemented in an urban sixth-grade class as well as during a sixth-grade field trip to the Barnes Foundation. The catalyst for this activity was an ongoing partnership formed between mathematics educators and art educators at the Barnes Foundation in Philadelphia, Pennsylvania. This partnership began with an email in which the authors asked the Barnes Foundation for access to diagrams used when the Barnes Foundation relocated from a suburban home to a large building in Philadelphia. Since that time, they have collaborated with art educators to develop field trip lessons and conduct workshops integrating mathematics with art in ways that align to the Common Core State Standards for Mathematics (CCSSM) (CCSSI 2010). (A bibliography is included.)