Many science problems require students to convert units. While this skill may not get the attention that more central science concepts do, teachers in the middle school and early high school grades will be doing their students a great service by leaving them with a strong understanding of both the skill itself and the reasons behind it. When the author taught eighth-grade physical science, he allocated time for instruction on unit conversion for density and speed calculations. Introductory chemistry also offers a myriad of applications for this skill. His approach centered on students learning the skill through a game: "Swap Meet." This article describes the game "Swap Meet" and suggests how a teacher can attempt it in his/her own classroom. The game gets students thinking about how unit fractions should look when a conversion is done properly. At a minimum, it requires about two class periods: one to introduce the game and let students play, and the second to transition from the game into more traditional unit-conversion instruction. (Contains 4 figures and 2 online resources.)