Engaging students in designing, testing, and revising engineering models using mathematical representation of data from scientific investigations helps them embody the science and engineering practices highlighted in the "Next Generation Science Standards" (NGSS Lead States, 2013). The practices of modeling, conducting failure analysis, and participating in evidence-based reasoning allow students to engage in engineering design processes beyond simple trial and error methods in solving a problem (NRC 2012; Bybee 2010). This article describes a unit conducted with fifth-grade students, applying Engineering is Elementary's (EiE) engineering design process or EDP (Ask, Imagine, Plan, Create, and Improve) to explore the lift force of a butterfly wing and the variables that influence it. EiE a project of the National Center for Technological Literacy at the Museum of Science in Boston, consists of curriculum units designed to foster engineering design thinking in elementary school children. The units are typically structured in lessons that include: (1) a story that introduces an engineering challenge and career; (2) a context for students to collect scientific data; and (3) an engineering design challenge applying the evidence gathered from the analysis of data.