This article presents a science, technology, engineering, and mathematics (STEM) activity, building an air cannon, in a mathematics classroom. It describes an investigation grounded in STEM concepts that elementary and middle school teachers carried out to think about ways of implementing STEM activities into their instruction. This particular activity has great potential for elementary school students in grades 3-5 in that it uses principles of science (force/energy), technology and engineering (building the air cannon), and mathematics (measurement and data). Such an activity can be worked into classroom instruction to "hit" on any one specific area or can be fully integrated to meet all STEM areas. One version of carrying out the air cannon investigation targets mathematics concepts specific to the elementary levels and is the focus of this article.